If you google "ESL reduced speech" or "reduced forms", you will find lots of examples. It's just how the words sound when speaking at a "normal" rate. They are not slang words. Here is one example website: http://jalt.org/pansig/2006/HTML/Brown.htm

السلام عليكم. هذا سوال ممتاز جداGreat question. Another example may be 'gotta'. 'Gotta' is used to mean 'have got to'. For example, one might say, "I have got to go to the store" or "I've gotta go to the store." I have also heard people say 'musta' to mean 'must have'. "I musta been sleeping when you called." "I must have been sleeping when you called." I have heard people say 'mighta' instead of 'might have'. I agree with Peachey. It is important to learn formal English. I am learning Arabic now. My teachers told me that it is important to learn the Modern Standard Arabic الفصحى because then people in different Arab countries will understand me. Learning formal English will allow you to communicate with many English speakers. I wish you much success on your studies. God bless you. مع السلامة

They're informal versions of "want to" and "going to". Other examples of this type are coulda, shoulda, woulda, oughta,

I believe that it is important both to understand the meaning of these words in order to comprehend dialog in stories and movies and to know that most English speakers do not use these words in writing or conversation.

"What is the meaning of 'wanna' and 'gonna'? Are there other words like them?" To add to Susan's answer, as a learner you really shouldn't use these. Learners who try to use slang before they know proper English end up with terrible English skills.