Some Modification Questions

[White_Snake]

hmm well, i been looking trought several products/plugins this days trying to learn new tricks and also i have some questions to ask that would be apreciated if someone help me to deal with em

1.- how can i introduce a new value on the array "post"
2.- what should i do to put into a conditional the id of a forum?
3.- which is the difference between this->fetch_field(foo) and $db->query_ etc etc
4.- about templates :i know how to use the <if = condition> and <else /> and </if> but, not sure about what i do to put into a conditional the userid of a user and the value of a usergroup

and i think are all, thanks for your time