solid help!

I waited until 7 months to introduce solids. He acted ready. He would watch us eat and reach for food. The problem he has is he isn't understanding to open his mouth. I don't think it's from not wanting the food. If he opens a little he loves the food. Smacks his lips and looks at the food bowl. I just don't know how to get him to understand how to open it for food. Any help would be greatly appreciated.