In British English phrasal verbs based on the verb to pop are extremely common in everyday speech. The basic idea of most of them is to go somewhere quickly or for a short time, as in pop out: 'I’m just popping out to buy a newspaper', and pop in: 'He popped into a café for a cup of coffee'. This is much more succinct than saying 'I’m just going out for a few minutes to buy a newspaper' or 'He stopped briefly to go into a café for a quick cup of coffee'.
Pop round, pop over and pop in can be used to mean 'visit', as in 'She popped round to see her sister' and 'Next time you’re passing, why don’t you pop in and have a coffee?' Similarly pop up and pop down can indicate short visits in the direction suggested by the adverbial particle (e.g. 'Pop down and see if the post is there, will you?' or 'I’m just popping up to the third floor to have a look in the electrical department'.). Pop up can also be used to mean ‘appear’, as in 'It’s only March but daffodils are already popping up all over the place' or 'He keeps popping up in the most unlikely places'. Finally, if words pop out, you say them suddenly without thinking: 'I didn’t mean to say that – it just popped out'.