Let me give you a complete run down of the whole economic system in starcraft.

First of all, you have to train workers constantly. If you even miss a couple of seconds of worker production, you're probably behind your opponent. And as AOE2 player you should know how this can snowball.

Then there is the resource gathering. A base has 8 mineral fields and two vespene geysers. Minerals can be directly mined by workers, and you need 2 workers per mineral field for optimal resource collection, but can be pushed to 3 to get less efficient mining. A structure has to be built on top of a gas geyser before you can gather vespene gas, but after that 3 workers can mine it for optimal resource collection. So on each base you ideally want 16 workers mining minerals and 6 workers mining gas. Another town hall is a huge resource investment (think if in AOE2 a town center would cost 600 food) and takes a while to complete, but faster expansions always lead to better economy later on. It's just that a player who doesn't expand usually has that extra money to construct a bigger force, and if you don't scout you can easily get overrun (greedy play).

Now workers will auto-mine if the town hall (command center for terran, hatchery for zerg or nexus for protoss) is rallied to a resource, and they will transfer to a different mineral patch if their current one gets depleted, but only on the same base. With the latest expansion pack, resources mine out pretty fast so you constantly have to check your bases if you don't have 3 or more workers per mineral patch, essentially doing nothing while not generating an idle worker count. Also minerals are used for everything, while gas is only used for tech heavy units or research, so if you mine too much gas you won't have enough minerals to support it and you will get a surplus of gas and a general lack of everything. There is also no resource-exchange like the market in aoe2.

Each race also has a specific macro mechanic. Terran has an ability on each upgraded town hall that can call down a time-limited super worker which ignores the above max-worker-limit and mines only minerals. The energy used for this is shared with the scan function which reveals a bit of the map (including cloaked units), so care must be taken to not use all the energy continuously as without scan some cloaked units can deal terrible, terrible damage.

Zerg can train units called Queens which have an ability to add to the production of larva per each town hall, which is used to spawn units (more on that later). This is also a timed ability and you have to roughly go over each town hall, and let the queen use this ability every 50 seconds or so. The queen can also place tiny structures called "creep tumors" which extend the purple mass on the ground (called creep). This creep gives a big speed bonus to all zerg units and is quite essential to get complete surround against enemy armies to actually kill them.

The protoss have an continous ability for each town hall called chrono boost, which can speed up any building. Either production or research times are decreased and it's a choice on which building (town hall = more workers, forge = faster tech or gate way = more units) to chronoboost.

Construction of buildings works for each race a bit different (Terran works like age of empires, but only 1 worker can build a structure at the same time, zerg loses the worker that builds the building and protoss buildings construct themselves after being placed by a worker), but the timings matter a lot. Build too many production buildings early and you won't have the economy to support them and you essentially wasted the money used to build them, build them too late and you will probably get overrun by the other player who does have enough production.

Supply (like houses) has to be built too. Terran uses supply depots which work the same as houses, while protoss make pylons which give a ring around them where protoss can only construct structures near (except for town halls), and zerg produces units called overlords that are flying heavily armored, slow moving units. They can scout and convert to dropships but if you lose one, you lose the supply too and can lead you to being supply blocked.

Unit production differs per race too. Terran uses the most traditional way where you construct barracks or factories and when they are complete you start training units, which appear out the side and move to the rally point. Zerg units are produced from a unit called larva, which spawn automatically next to each town hall and they are capped at a max amount. A queen can be used to temporarily increase that cap. Protoss at first have gateways that work like barracks, but they can be upgraded to warpgates, which allow them to spawn units in the field of a pylon anywhere on the map, after which they enter a cool-down period. Air and specialist units are still produced like barracks though.

And finally upgrades. A simple +1 attack upgrade can mean the difference between an equal fight and a decisive victory. Some units also one-shot other units with certain upgrades, which is incredibly important for small skirmishes or worker harassment. A lot of units have upgrades that can give abilities to certain units (like blink which allows the basic protoss ranged unit to teleport a small distance every few seconds) which can give a very big micro potential. Also support units like medivacs (flying craft that shoot heal beams to friendly biological units) and incredibly important, so a good balanced army composition takes a lot of preparation while building stuff.

Now the most important thing is because the distances between town halls and resources is always fixed, workers running around is a lot worse then workers in aoe2 walking around. Sure you can build additional resource gathering points near the resource you're mining, but eventually the workers will spend more time walking then actually mining resources. In SC2, if a worker is moving it's not gathering resources, and that's always bad. Sending out a single worker to scout has a noticeable effect on your economy compared to one who doesn't scout, and even stacking workers correctly in the early game (getting 2 workers mining from the nearest patches to a town hall) can even make a difference.

And that is probably the difficult part that you're missing.