I'm not a talker. Growing up I preferred to play alone. In school some people thought I was snobby because I didn't talk. Now when people introduce themselves, I'm doing well to remember to say my name. It's just so much easier to listen while other people talk. Spoken, on the spot words are hard.
So when God gave me the task of talking to someone I didn't know about something I knew nothing about, I wanted and tried to replace me with someone else. It was very much like when Moses told God he wasn't the right one to talk to Pharaoh. Moses didn't speak well (according to Moses), so it was just best for God's plan for God to pick someone else.
However, when I (and Moses) claimed, "God, I'm just not able," God responded, "I Am." I heard and absolutely believed God but still tried to offer a better speaker as my substitute. Thankfully God removed that option and gave me two options: either you obey or we aren't doing this. On the spot I prayed for help and obeyed.
God is going to ask you to do what you are not able to do. If you try to follow Him at all or even just say you want to follow Him, God is going to challenge you to go into a situation you are not equipped to handle. When that time comes, remember to stay with God, confess that you are not able, and listen for God's answer: I Am.