I have a model, and I accidentally deleted some vertices, and I need to get the surface back. The hole is outlined in red in this image. I have 5 vertices and have no idea how to make the surface.
Since your mesh is triangulated, you should create three triangle faces. For instance you could connect them in the following pattern.
In order to accomplish this, switch into Edit Mode (TAB) and enable Vertex Select.
Select the three vertices (and only the three vertices) that are supposed to form a face. Once they are selected press F to create the face. Deselect the vertices (ALT+A) and repeat with the next three vertices.