OP: Look up your Job here
https://www.thebalanceffxiv.com/
It tends to have a general overview that explains things. Note that it uses the level 90 abilities, so if some abilities upgrade, you might have to open your Actions and Traits and figure out which ones do. Sometimes it's kind of easy like WHM Stone becoming Glare and just having the spell ranks, but other times it's a bit more confusing, like BRD's Straight Shot becoming Refulgent Arrow (I think...), but if you can manage that, the guides there give you suggested openers, which tell you when to use your party buff (after the first time, you use it on CD unless the boss goes untargetable and you hold it for the "reopener" when they come back), and the guides also will give you some explanation of the nuances of the Jobs.
Oh, also, if you want a "preview" of Jobs, you can go into PotD and que for the floor 51-60 runs, and you can unlock PotD at level 30, I think? You need your Job stone to see the Job's abilities, but once you have that, going into PotD you can play with the level 60 kit. Which...is a lot less than it used to be, but is something. HoH and Bozja (sorta) and Orthos also all allow you to play around with more of the kit, but if you're low level and trying to see if a Job might be a fit for you, PotD is good for giving you at least a BASIC idea oof what it does and some of its rotation and abilities. Nothing is perfect, but it's not a terrible way to dip a toe in and test the waters of a Job to see if you might like it.[...]