Learn Turkish: Masada bilgisayar ve telefon var. - There is a computer and a telephone on the table.

In Turkish, the word expressing existence like var (there is/are) almost always goes at the very end. The standard word order for pointing out where things are is: Location + Item(s) + var.

How does masada mean "on the table"?

Masa means "table". The -da attached to the end is the locative suffix, which tells us where something is and translates to "in", "on", or "at". So, masada means "on the table".

The English translation says "a computer and a telephone". Why aren't there any words for "a" in the Turkish sentence?

You could say bir bilgisayar ve bir telefon to strictly mean "a computer and a phone". However, Turkish often leaves out bir (a/an) when just listing general everyday items that exist somewhere. It's perfectly natural to just state the names of the objects!

Since there are two things (a computer and a phone), does var mean "there is" or "there are"?

It means both! Unlike English, which changes between "there is" and "there are", the Turkish word var never changes. You use the exact same word, var, whether you are talking about one single thing or a hundred things.