I have logged an infeasible number of hours on roll20 so can probably help out. You can do some of the following:
1. On the table landing page (before you actually enter roll20) you will find a settings button. Click that and go to game settings. Compendium setting (the rules stuff) should say determined by character sheet. That is fine. Scrolling down you can select Share my Compendium with players and also set to allow players to import sheets. Further down you can set the character sheet, set it to D&D 5E Community as that seems to be the most common. Personally I just write macros as I find they are much simpler but lots of people like to use the sheets.
2. Once you enter the roll20 table you can either create a character sheet for your players or they may import them. Nothing requires a player to import or use a sheet, they could just write macros in the Collection tab.
3. You can provide players with a character sheet to use in the Journal tab. Select Add character. I would start of creating one for each player, set them so they can both be edited and are in the journal of all players. Once a player has claimed one you can change that to allow only them to access it. Once a player has claimed a sheet they can upload their own token to represent their character if you want them to. They simply hit edit and in the avatar box select click to upload.
4. I like to create folders on my table to store things, I tend to create one for handouts, PC character sheets and enemy character sheets.
5. As I say I don't tend to use the character sheet for dealing with stats and dice rolls, I automate things with relatively simple macros. Roll templates organise things a bit more neatly. Different character sheets support different roll templates. I am not familiar with the 5E one but the default works reasonably well. A simple one might look like this:
&{template:default} {{name=The Rogue attacks!}} {{Club [[1d20 + 10]] for [[1d10+4]] damage}}
You can get a bit more fancy, adding conditional modifiers like this:
&{template:default} {{name=The Rogue attacks!}} {{Club [[1d20 + 10]] for [[1d10+4 +?{Sneak attack|2d6} ]] damage}}
Fancier still?
&{template:default} {{name=The Rogue attacks!}} {{Club [[?{Advantage|Yes, 2d20kh1|No, 1d20} + 10]] for [[1d10+4 +?{Sneak|Yes, 2d6|No, 0}]] damage}}
Personally, for monsters, I don't put the attack roll into the macro for players to view. Mine might look like@
&{template:default} {{name=The Rogue attacks!}} {{Club [[?{Advantage|Yes, 2d20kh1|No, 1d20} ]] for [[1d10+4 +?{Sneak|Yes, 2d6|No, 0}]] damage}}
/w gm +[[10]]
The basic initiative macro looks like this:
&{template:default} {{name=Prepare for battle!}} {{Initiative = [[1d20+5&{tracker}]] }}
Obviously change the number to whatever the right modifier is. If you have the token selected when you hit the macro it will add the character into the turn tracker. If, when making the macro, you select only "token action" then you have to have the token selected to roll the macro.
You can find a lot of stuff on using roll20, sorting maps etc here:
https://tarrasque.wordpress.com/
If you have any questions I am happy to help. If you want to have a look at one of my more complete tables join this one:
https://app.roll20.net/join/5160925/u2tm9A
It is for Pathfinder 2E but it will give you the idea. Let me know when you have joined and I will promote you to GM then you can see everything. I have a pro level subscription for the storage space so if you want me to create a table so you can use the features let me know.
Andrew