On the right hand side you have "like" "quote" and "reply". If you want to use the whole post from a previous poster you just press the "reply" tag. If you just want snippets then you press the "quote" tag. Long press on the part of text you're interested in and it highlights it in blue and quote signs appear. You just move the quote signs by long pressing and moving them about to cover the part you want. When you've done that it'll say "reply/quote". Just press the quote bit and the part you've highlighted will be saved into your post. If you want multiples you just repeat using loads of people's different posts that you want to use. It's tricky at first.
That's how I do it anyway. It took me ages to work it out, i'm useless with tech stuff.