Another basic pensions question

[thismonkeyhere]

I feel I should probably know this, and if not then I should get professional advice, but in the meantime:

After the end of my service career, during which I paid attention to only one pension aspect, I now find myself making my way in the world in 'proper' jobs and so far, and forecast, I have been/will be moving between organisations every 2-4 years, and so will end up with a bunch of small pension funds.

Should I merge these into one somehow?

If not, what happens at retirement time? Does one just add up all the little funds to reach a total with which to buy an annuity?

Thanks.