about Taps?

Dear Sir, My Bathroom sink Basin has a lever type tap, sometimes the cold water runs for a few seconds and then stops,it does this proceedure at any time of the day,sometimes there is nothing at all coming out...
I would be grateful if you could help us as both my Wife and I are 84.yrs old and we do worry when these things happen,also we have to try and do things ourselves as it is so costly when you get a professionaal in to do a job. Sincerely R.Bray