These are caused on normal basis and if you do not have pretty much knowledge on what these are and what these error means than check out below errors.
400 error is simply a bad request error, as you might be typing some unknown URL that server could not understand, so make sure that URL you are typing is write.
If you try to access some unauthorized website than you might see this 401 error, so make sure you have entered correct username and password.
402 error is specified for any kind of payment errors you receive, so if you attempting any transaction and you forgot to add payment information than you might face this error.
403 error can cause if you are accessing any forbidden page s its somewhat similar to 401 error, so make sure you are not blocked by that website.
404 is the most common and most recognized error, so its like most website have this error, so that website might be removed or re-named so make sure spellings are good.
408 error is the timeout error, so if you are on some page where it requires you to add something in specified time and you do not do that than you might face this 408 error.
Well now there were the few errors you might face, and possibly you have some good knowledge on how you can bypass them and enjoy your internet browsing.