bussin should be interpreted as busting (it's written as "bustin" on Gucci Mane's t-shirt in the official video of the song).
juugs is also sometimes spelled joogs. I believe it derives from the word "drug". As a noun, it seems to mean something like a small-time drug dealer, or the act of selling a small quantity of drugs. It can also be used as a verb which means to engage in the activities of a small-time drug dealer (for example, when Gucci says "I juug so good").
It is used in all of these ways in the song:
- You're just another juug [small-time dealer].
- I juug [sell small quantities of drugs] so good.
- When I came back to the city bussin juugs [committing small-time drug deals]
In the song, Gucci Mane seems to be describing his life as a small-time drug dealer. In the chorus, his girlfriend says to him that he's "just another damn juug," to which Gucci responds that he's more like a plug, a higher-up drug dealer or supplier.