Starting a new wallet is as simple as typing in a new seed. Keep this seed safe and never share it with anyone as it is the only way to access your wallet.
Seeds can only consist of capital Latin letters and the number 9. The maximum length of the seed is 81 characters and it is recommended you use this length.
You can generate a suitable seed within the GUI by selecting ‘Tools -> Generate Seed’.
If you don’t want to use the GUI you can execute the following Code in Linux or OSX to get a new Seed:
cat /dev/urandom |LC_ALL=C tr -dc 'A-Z9' | fold -w 81 | head -n 1
Copy the seed and store it somewhere safe - remember, if you lose it you will also lose your IOTA! We recommend that you print your Seed and remove it from your computer (this is the safest way).
Wallets are deterministic which means that every address generated will always be linked to and recoverable by your seed.
This tutorial and others can be found at http://www.iotasupport.com