How do I add features to my terrain?

How do I put ground features such as grass and dirt on my map? I am not really sure what i need to do for this a little help would be appreciated. Also I would like to make the tree’s in my map more treelike so to speak and unable to walk through.

To fix your tree issue, check out this question. Don’t forget to search (here and google) before asking about these things.

As for the features you want to put on your map, check out the reference materials on the terrain editor. It’s the first result from a google search for “creating grass unity”.