There are several ways to create an EOS account on Wombat. One would be launching any EOS-based dApp or game, like Chain Clash. Another way is to go to Settings, tap or click on EOS in Keys & Accounts.
In both cases, Wombat will automatically take you to the account creation screen. You will need to pick an account name of 12 characters. It can only include Latin letters and numbers from 1 to 5.