To vote, you wander up to your polling station and give your polling card to the election officer (if you forgot your card, you just tell them your name and address. In-person fraud is so un-British that it just doesn't happen). They look up your name in a list, go "boggyb, right?" and record that you've turned up. They then give you a ballot paper.
You take this ballot paper and head off to one of the booths. Most UK elections use the first past the post system which means that to vote you put an X next to the candidate you want. The police & crime commissioner election used the supplementary vote for a change, which means you put an X in column 1 for your favourite candidate and if you wish an X in column 2 for your second favourite candidate. If there's multiple elections happening (the usual combination is local and general), you get one paper per election. Simples!
You then fold the paper in half and drop it in the ballot box. Officially you're supposed to show the back of it (with the ballot number) to the election officer, but the ones here have never been interested in that.
That's it. Later on at 10pm they will stop handing out ballot papers, and once everyone who's got one has voted the boxes will be sealed and taken somewhere to be counted. There they will be leisurely hand-counted and a result usually declared mid-morning the next day (unless you're Sunderland, in which case a small army of students will frantically count them in an attempt to be the first location to declare a result).