My clearest memory of Teletext is how slooooow and unreliable it was to load anything. But I sat it out and waited. Compare that to now where if your website takes an extra second to load then you can lose like half your traffic. Everybody was much more patient with technology back then.
There were also interactive pages where you could phone in and press numbers to access a much larger set of information. You'd get your own temporary page number (that anyone could technically see), and the teletext broadcast equipment would insert your updated page into the stream when you pressed a number.
You would dial a premium rate number and you would then be read out a page number. You went to that page and used your telephone keypad to do interactive stuff and the page would update in near real time. The two biggest things were managing your Sky fantasy football team and banking from the Co-operative bank.
Our TV had a function to let you see all active page numbers so I would often go and spy on what other people were doing.
There was a short period where you could download games from Ceefax, although it required special hardware.