I need help figutring out how to get a form online to be filled out on my computer?

hi, i have some applications and forms online to fill out and also an application sent to me to fill out. I download and open the attachment but then can not fill in the forms ata ll it will not even allow me to type! I hit keys and nothing happens, i really a new to computers and can not figure out why this is happening and what i can do. It says doc at the bottom of how they sent it the attachement. I have also tried to fill in a resume online and the same thing can not do anything and not type to fill it in either. A man said well you have to delete the line then type i hit delete and still nothing, easy terms please on how to do this it is important i figure it out. Thank you.