Hi karolex5, welcome to GPS Power.
I see this is your first post, so I'm not sure how experienced you are.
A good starting point is to have a look at our tutorial section first: [Only registered and activated users can see links. ]
Here you will find the answer to most questions you may have.
The specifics how to place map files on a (micro)SD depend on what model GPS unit you use.
Please elaborate and we may be able to point you in the right direction.