Hi there
@Shahba and welcome!
I'll go things in order, keeps things simple / layman's terms, and others can advise / correct as necessary
1) The competitions you receive games for may or may not require the teams to give you a list of their starting XI, and in nearly all circumstances will require you to obtain the names of the (non-starting) substitutes. Sometimes you won't get a team-sheet, sometimes you will, ensure each match you DO get the sub's names (unless you're on leagues with roll-on, roll-off "return" subs). Either way, if you do caution or send-off a player, substitute, or team official... you'll be asking and confirming their name at that point. If you're not given a 1-11 teamsheet before kick-off, crack on. But do ask ahead of kickoff for their named subs.
2) Matches will NOT automatically appear on WGS in most circumstances. As a new referee, I wouldn't expect them to, and neither will it act as an "I'm busy that day" reminder to any other league/referee secretaries when it comes to giving matches out, so you'll need to stay on top of your availability if you ref for more than one league. You can either Add Match yourself ahead of time, and select the teams and competition involved from the search function and drop-down boxes. This may be helpful or not if you want a form of diary, OR merely add the fixtures after completion. No reports? Then select 'No Reports'. If there's been misconduct you need to report - cards, other nonsense - then can add the fixture at that point and go from there. It's all quite straight forward when you get to it, and we'll all be happy to help if you get stuck.
3) If you've had no incidents in a match, then you can opt to not Add Match on WGS.. but best practice is to Add Match, fill in the form, and then there's "No incidents to report", where you can simply select that and submit a "nil report" meaning that your FA knows you ref'd the game, and have nothing to report. Yoou're not responsible for line-ups, teams, scores, etc. These are wholly the responsibility of the club(s). As a ref, purely misconduct (yellows / reds / if anything else happens). Breaches of COMPETITION rules should be reported to the competition secretary (late kick-off, no technical area, no corner flags, no club lino, etc etc) and not through WGS.