Welcome
The wiki has step-by-step instructions for importing a GEDCOM file.
Getting started with Gramps can have a steep learning curve. You can save a lot of heartache by watching a couple of the free video tutorials that various users have created.
For your particular question, the 2nd TechTutorials YouTube video covers importing a file. The .ged (GEDCOM) format import is done the same way as a .gramps format file.