I need to add a grid on a map I created with my own layers and GPS data.
How can i do this?
I know how to do it in Arcgis, but not in QGIS.
If you only need a grid for your print layout. That's possible in Print Composer. Check the map item's properties for grid settings
If you want an actual grid layer in your QGIS project, you can create one from Vector menu.