Do you have a programme associated with the files in order to open them?
Right click on the file you want to open, click on open with, and then choose. If you do not have an "open with" then click on open - select a programme from a list of installed programmes - ok
if the programme you want is not there then under other programmes click on the down arrow on the right to expand it and you should see more options.
Don't forget to click ok.