I would recommend looking at the API scripts page for your campaign, and the one-click installer. There's a bunch of scripts that are useful to install there. First I would suggest is installing TokenMod, and setting up a couple of macros: one for updating pc tokens, and another for npc tokens. You'll have to look at the syntax to figure out exactly how to do it for your campaign, but this will enable you to drop a token on the map, change which character it represents, and then click the tokenmod script and immediately set it up as the default token for that characetr, with all token settings you need applied automatically. This is a massive time saver. I'd also recommend you look on youtube for roll20 tutorials, read the roll20 wiki, and do the roll20 tutorial. If you really have no clue what you're doing, most people's advice (like that i just gave you) will likely confuse you. You need to know some basic stuff before you can really take advantage of people's help.