'Jolly well' literally means very good: you could say 'jolly well done'- meaning you have done very well. You could say 'he did jolly well': he did very well. However it isn't a phrase that is used often; everyone know's it but it's used as more of a exaggerated way of saying 'very well'. If you want to say 'sure' you could say 'of course': e.g Can you buy some milk for me? Of course I can You could say 'certainly': this is perfectly fine but most people would use sure of 'of course'. hope I could help :)

I take it that you've been reading Enid Blyton again? Or other British writers from the mid-twentieth century? 'Jolly well' is an adverbial phrase used to add emphasis, sometimes indicating annoyance or irritation. For example: 'Where's my book gone?' 'Johnny borrowed it, and .. um .. I think he's lost it'. 'Lost it? Well, he can jolly well find it again!' This is quite old-fashioned, from the days when swearing was less permissible than it is today. A less 'Enid Blyton-ish' way of say this might be the equally British but rather less polite 'He can bloody well find it' or the more American 'He can darn/damn well find it'. Whatever phrase you use, it's just there to add emphasis. The comment means 'He'd better find it!' , but it's stronger than that. The implication is 'He'd better find it ... because if he doesn't, he's going to be in trouble'. Do we still use 'jolly well' in this way nowadays? Sometimes. I do, anyway. It's a good way of being emphatic without actually swearing.