Yes, they just turn a key to open them. Some staff have ticket-sized cards that open them, or a smartcard that opens them.
Valid tickets may be rejected by barriers, and invalid tickets may be accepted by barriers. Ticketing in Great Britain is extremely complicated (the routeing guide has several thousand pages and includes a hundred or so maps), and magnetic strip tickets only hold something like 8 bytes of data. Although some tickets are now e-tickets in the form of barcodes, it seems that train companies have not invested in improving barrier programming.
Barriers can be set to reject certain tickets for revenue protection purposes, often used to force railcard holders to present their railcards to a staff member for inspection.
When no staff are available, barriers must be left open, as passengers must not be left inside stations unable to exit. In case staff forget to do this, pushing a barrier forcefully will also cause it to open.
Some barrier lines only have staff available by video link.
The strips can lose data too. Bought tickets return London Bridge to Gatwick. Returning at Gatwick, the barriers wouldn't open so had to get staff to let me through, same at London Bridge end. The printed details were correct on the ticket so I can only assume the details got wiped off the ticket. It was sitting with my other cards in my passport wallet while way so that may have demagnetized it. My brother stayed in a Novotel recently and his door key got affected by this as he put it with is credit card in his wallet. Which is the natural place people would store it when out of their room....