This simple phrase has a lot of interesting aspects. Notice how, because of the /k/ sound of “complain”, the end of “Can’t” changes to /ŋ/, which is made using the back of the tongue; the same place as /k/. There might be a slight stop between the words, but keep the back of your tongue in place. Also, it’s important to notice the weak vowel /ə/ on the first syllable of “complain”.
The phrase is a reply to the question “How are you?”, and means “I’m OK.”