Use them only if the other person you are speaking with uses them as well. This means listening first. Don't ever use them in writing unless you're quoting someone who used those forms. Also, be careful of making horrible grammar mistakes. The "-na"(to/a) part must connect properly to the following word, otherwise you'll just sound silly, even to a casual speaker. If in doubt, just use normal English. No problem with that.

the same like the original verbs but with no "to" and becareful they're used in informal speech WANNA i wanna go home. You wanna eat now? it can also use instead of "want a " Wanna drink/slice of cake ? GONNA i'm gonna kill you. you're gonna love this.