NanKate, I can only give you hints for the desktop site, but if you scroll to the very bottom of your iPad screen you can select 'desktop site' to follow my instructions then revert to mobile site, also at the very bottom.
Open any thread and you will see that at top and bottom on the right of the line where the page number is shown is an option to customise. Select yes to the question about bookmarks.
From then onwards you have only to hover over the bottom right of a post until it displays 'saved' or 'bookmark'. Click on the word and you will find next time you read the thread you will be taken to that point - very useful.
Sorry this sounds so involved. I waited for someone to answer simply but no joy!