y does this paint in square how can I fix this? how do I paint the hole thing with one click??? like a fill map?
Paint over the entire terrain with one layer -> after that it should work 
oo ok I guess ill do that thanks. how do I paint the hole thing with one click??? like a fill map in button or something?
Just choose a large brush + a paint strenght of 1
cool thanks. does this program come with grass meshes or other type of meshes other than the plain squares?
No, but here is a free foilage pack that I made.
You can find more free assets in the learn tab of your launcher.
how do I open this rar type file and where would I save this files for use?
To open a RAR file you will need a program such as 7-Zip or WinRAR. 7-Zip is the simplest one to use and allows you to extract many different archive file types, you can get it HERE.
So with 7-Zip installed you can right-click on the file, go to the 7-Zip menu and choose “Extract to FolderName” or “Extract Here”, then copy the files it generates into your ProjectName\Content folder.
Also take a look at this video:
You just have to extract the rar file and after that you can open the project. When you want to move the assets to your own project, follow the video above