Solids

I need advice on solids. We have given broccoli, his favorite, spinach and egg. How would I know if something is not sitting right with him? Are green poops, and some mucus normal. To note he is 6 months and already has two teeth, and I think the top ones want to come in too but not sure. Then what solids is everyone startibg with, we don't want to do sweet things first, for those that waited, how long till you introduced sweet food - sweet potato, fruits, that kinda sweet food. What did you give first? Also when do you start giving more food and tougher?