Fundamentally REDCap will consist of several projects, each being a self contained set of questions. The questions are grouped into sets (defined by the user) called instruments. Each user can have access to one or many different projects, each with whatever level of authorisation you want.
When you first start a project it is in development mode, you can add fake data as much as you want to this while you sculpt your questions. When you are happy with your instruments you move it to production, THIS DELETES ALL THE DATA IN THE DATABASE. Editing the instruments once you have started is probably a bad idea (what happens if you change a data type?), so don't do it.
SQL field type
A useful, but specialised, field type is the 'sql' type. It allows for a database query to populate a dropdown.
Full details on the REDCap wiki at https://iwg.devguard.com/trac/redcap/wiki/SQLFieldType
Implementing the sql field requires that the table housing the data is stored in the same database as the REDCap tables.
More details on sql fields contained in LCBRU REDCap implementations are on their own page: REDCap sql fields
It should automatically detect the device that is being used to view the pages, so if it is a mobile device (tablet) you will get the mobile version. To see what it looks like on a real computer use a URL like yourhostname/redcap_v4.5.1/Mobile where the version number is from your install.
The web interface lets you export the data in a variety of ways; CSV, SPSS, SAS and R. It also lets you do more useful stuff with the API.