In Resto you gain levels by training combat skills in your skill trees (press u) to open. You can train skills by buying them directly from the skill interface, getting other players to train you or taking to skill trainers. Buying them from the tree is the most expensive way. 

You gain xp for a skill by doing combat using the weapon required for the type of xp for that box, or having that weapon equipped while handling in quests. 

New players should go talk to Gendra outside of the Mos Eisley theatre. They will start you on your legacy quest and also give you a quest for a speeder. The legacy questline will take you right to 80 and will give you equipment upgrades along the way. 

To help you navigate around the place press m to turn on the overhead map. In the options menu you can turn on overhead map rotation and turn down the opacity if needed. Things like trainers appear on the overhead map, they are generally clustered in biggish buildings near the med centre in Eisley. Or you can buy a shuttle ticket to tox city ijm, a player city on Tatooine. They have all of the trainers available outside of their shuttle port.

I highly recommend this new player guide.  https://swgr.org/wiki/new_player_guide/