They are synonyms. There is no difference between them, you can use them interchangeably.

We can use the verbs begin and start to mean the same thing most of the times. Here is what I find that you can use start, but not begin. 1. We use start, but not begin, to talk about machines: Press this button to start the printer. √ Not: …to begin the printer.× The lawnmower won’t start. (this means that it doesn’t work) √ Not: The lawnmower won’t begin.× 2. Start, but not begin, is used to talk about creating a new business: She started a new restaurant and it’s been going really well. √ Not: She began a new restaurant … × http://dictionary.cambridge.org/grammar/british-grammar/begin-or-start?q=start …………………………………………………………………………………………… Start, but not begin, can also mean ‘to start a journey’, ‘to start something happening’ or ‘to start a machine working’: We’ll need to start at 7.00. Who do you think started the fire? The car won’t start. http://www.oxfordlearnersdictionaries.com/definition/english/begin?q=begin

Thanks Janet (good explanation) and Charlescuy

You can also use start as a noun. I don't think you can use begin as a noun though.

These are very similar verbs meaning to initiate. But I will tell you in certain instances it "sounds right" to use one instead of the other. What quickly came to mind ... I would say "start over" but I wouldn't say "begin over," I would say "begin again." One would definitely say "start the car" (or other equipment) and I think this topic was recently covered well on this site. Another example is when someone warns "Don't start something with me!" meaning don't argue with me. In this context one wouldn't really say "Don't begin something with me!" There are probably many other examples.