Did you setup a database environment and if so which one? sqlite3,
Check your database.yml in config and it should appear like something
similar for development:
Check the adapter and determine if you are using the right type of
database environment. The default for rails is sqlite3.
Let's say for instance that you want to use sqlite3, you need to make
sure that you have the gem installed (sudo gem install sqlite3-ruby) for
linux, or gem install sqlite3-ruby for windows.
You also have to make sure that you have the latest sqlite3 files
installed on your system. sqlite3.exe, sqlite3.dll, sqlite3.def (I
place these in my Ruby/bin folder since Ruby/bin is added to my path
environment. You can choose to place them anywhere so long as your path
environment can find them.
That solves sqlite3.
However, if you are using mysql then you need to do the following:
download the gem:
(linux) sudo gem install mysql
(windows) gem install mysql
Make sure you have mysql installed on your system and setup and that the
server is running (mysqld).
Restart your rails server and click the tab (should be good from there)
Let me know if you need any help with this. It can be a little tricky
to get used to at first.