I haven't played in nearly 20 years, but back in the day I had to explain the mechanics to a lot of people who were coming from MTG. The key differences are:
It (usually) doesn't cost a thing to put a card into play. Energy ("lands") is attached to the creatures to power up their moves.
The number of creatures you can summon is limited to 6. Of these, one is "active" (attacks and defends) and the rest are waiting in the "bench". You can switch out the active creature, but it often has a cost (discarding energy). You can't not have an active creature; if it dies and there's no one to replace it, you lose.
"Evolution cards" are just upgrades played on top of summoned creatures. They tend to be more powerful but also need more energy.
Any other cards that wouldn't be creatures or lands are "trainer cards" and cost nothing to use. However, you can only use them during your turn (here countering consists of preventing your opponent from doing something).
3 ways to win: the opponent is left without any creatures, the opponent's deck runs out, or you draw all "prizes" (6 cards set aside at the beginning of the game, you draw one every time you kill a creature).
tl;dr: It's kind of similar to MTG, but a bit more relaxed and completely centered on creatures.