Take a look at the following two sentences - which one is correct and why?
Are you interested in studying English?
Are you interested in study English?
That's right, the first sentence is correct. But why?
When the prepositions in, at, with, of, for, about and so on are used before a verb, the verb must use -ing.
Let's take a look at some other example sentences using prepositions + -ing:
'I'm scared of swimming in the sea.'
'Thanks for giving me a ride.'
'My brothers good at playing tennis.'
'How about taking the bus?'
'I'm not interested in reading books.'