My main piece of advice is: Be very careful!
Some very reputable universities indeed offer degrees by distance learning with most of the work done online. These are probably on a par with residential courses as far as content is concerned, though you miss out on the informal discussion with your fellow students.
However, there are many 'online universities' offering 'degrees' that have no value at all - in some cases you merely send them anything from a hundred to a few thousand dollars and they will send you a pretty degree certificate by return.
You will need to do a lot of research on the institutions themselves - and remember that online institutions having the words Oxford or Harvard in their name may have no connection at all with those real-life universities.
Also, do not be fooled by institutions claiming to be accredited. The 'Accrediting Body' may be as fake as the university itself.
- For Teachers