If you're not sure if you want to do it, then don't it. If you' were sure... you'd be sucking cock by now.
Just take some time and figure out what's holding you back. Denial? Internalized homophobia? Whatever it is, work it out.
There's no rush. There's a never ending supply of cocks to be sucked but cocksucking is not something you should approach apprehensively. When you want to suck cock, you'll know.