I find opening the reply composer in the topic I want to reply to and then navigating to the topic(s)/post(s) I wish to quote is a good flow.
Though the new ‘copy quote’ button allows you to copy the quote along with the correct quote formatting to paste it into your reply if you want to do it the opposite way round.
If you’re looking for beginner tips like oneboxing you can do the Discobot tutorial or possibly look at the Discourse New User Guide?