Posts can be a longer chunk of text, used to voice ideas and opinions, and spark discussion! Posts can be commented and you can like posts and comments alike.
Polls allow people to cast their votes for a selection of options. Creating posts in the Chatter feeds of Plans and Decisions allows you to scan the opinions of others. With the help of others, you are able to make better decisions together!
Questions allow you to ask anything and choose the best answer from the bunch. You can also ask questions in the Chatter feeds of Plans and Decisions. Do not forget to tag all the relevant people with the "@" symbol in the question.