I yeah - You say it when you don’t know the answer, but you also don’

You say it when you don’t know the answer, but you also don’t want to admit it, so you just make it up.

'What’s the capital of France?' 'I yeah, and it’s pizza.'

'What time is it?' 'I yeah, and it’s whatever time I say it is.'

'What’s your name?' 'I yeah, and it’s the name you’re gonna forget.'