You're gonna be thrown a lot of information as a new Portmaster. I'll give you some of my tips that helped me through the first few regions:
Herblore is a great skill to unlock your first adventurer (possibly the best). You'll unlock the Biologist who will gather you Ancient ceremonial bones as a trade good (however this will not happen for some time). These are used in making Scrimshaws, the most valuable reward for both money making and combat. They are also used ad a primary ingredient for Death Lotus Darts. Now that you know what you are looking forward to, let's start with what you'll actually be doing your first month.
The first region will allow you to collect Bamboo. After you've hired a captain and some crew you'll want to start sending your ships to gather either bamboo or coins (most often times both). Coins will be used as a secondary cost for most everything around the port, but Bamboo will be what you need to farm. Voyages typically only last 20-30 minutes so make sure you are close by the portal. Doing things like small slayer tasks, Herb runs, lights skilling will keep you occupied while you wait. It's very important that you send as many voyages as possible even with high adversity. All missions besides Story Missions (explained later) will still count towards distance traveled- even failed missions. More distance means sooner unlocking new regions and thus new resources and captains/crew.
You can use bamboo to upgrade several things around your port. Here's my suggestion for priority:
If you go in order you will likely hit the next region by the time you start farming resources to upgrade cosmetic things like your Entrance Portal. This applies to most all regions- even high-level ones.
There are some exceptions to this depending on each regions and crew accessible