The gain command is used to learn new skills, once your guild master has been found. Trains (and not practices) are used to gain new skills. Rememeber that yu must be with your guild master to check your gain list.
Gain list - Typing "gain list" lists all groups and skills that can be learned.
Gain <skillname/realm/sphere> - Typing gain <skillname, realm or sphere here> adds a skill or skill group, at the listed cost.
Ex: Gain sword (allows you to learn the sword skill).