You should not rashly buy what you do not know, it seems you need to learn a lot before starting.
1. Trustwallet is a wallet, not an exchange. You may find the DEX page, but it has a limited list of coins/tokens. You can only buy the tokens you want on third party DEX platforms that allow you to connect your trustwallet like Uniswap, pancakeswap, 1inchswap, etc. Each DEX may have a different swapping procedure, you will have to find a tutorial on using which DEX you prefer (
eg. Uniswap). First make sure in which DEX that token is listed. Currently trustwallet supports multiple tokens based on multiple networks (
read more) and of course you can accommodate all of them with 1 trustwallet.
2. Good if you start with a small amount. Different networks, different transaction fees. Afaik, for now there is no comparison site on token transaction fees of all networks, so you will have to look for a specific site that gives you information on current fee estimates. But when you are about to make a transaction, the trustwallet also informs you of the required fees before agreeing to it.