To get started, you'll want to get familiar with Foundry's user interface. Characters can be made on the Actors tab, but see the image below for a quick run down of what those tabs in the right sidebar are.
In order from left to right:
1.
Chat Log - Where all chat messages and power card rolls are displayed.
2.
Combat Tracker - Track combats and combatants. Scenes can have multiple combats, and each combat will have its own escalation die.
3.
Maps/Scenes - The scenes where you can place maps and prepare for sessions.
4.
Actors - Where your custom characters and monsters are created and stored.
5.
Items - All item types that can be placed on actors, such as Powers or Magic Items for characters or Actions for NPCs.
6.
Journal Entries - Journal entries where you can store notes that can later be placed on scenes.
7.
Rollable Tables - Your custom rollable tables.
8.
Music/Playlists - Foundry's music player that can be used to control your playlists.
9.
Compendiums - Compendiums of content in your world. The system comes bundled with compendiums for each of the classes, races, and monsters in the Archmage Engine SRD.
10.
Settings - Settings for Foundry, the Toolkit13 system, and your modules. The system includes a handful of settings that you can use to tweak it, such as average recovery rolls and a colorblind mode for accessibility.
To make either a character or monster, go to the Actors tab and click the Create actor button. You'll then be prompted to choose the actor type you want to create, a Character or an NPC.