How can i fill in forms on attachments on computer?

hello, I have applications online sent to me to fill in and also on job sites and when i download the forms and try to then fill them out, nothing happens, i can not even get computer to type. one person said i need to delete the line then fill it in, but when on the forms will not allow me to type. What must I do to be able to fill in forms? They are usualluy sent in doc. i need help please, also can not get resume online toallow me to fill in those blank lines either???? Thank you.