This article explains how to find the forehand grips in terms that you might find interesting and helpful, but the following, more recent article will likely lend a quicker understanding:
Before we start talking about Continental, Eastern, Semi-Western, and Western grips, we need to establish points of reference on your hand and on your racquet handle.
A popular and adequate point of reference on your hand is the "V" between your thumb and index finger. I prefer to use the base knuckle of your index finger, because its position will correspond to that of the center of your palm. The key differences between grips are the different angles they create between the angle of your palm and the angle of your racquet face. You are used to sensing the direction your palm is facing, so your palm makes the most intuitive basis for sensing the direction your racquet is facing.
On your racquet handle, let's start with the plane that is horizontal when your racquet face is vertical. If you set your racquet on edge on a table, this is the plane of your racquet handle upon which you could look straight down. We'll call this the top plane. To the right of the top plane is one that slants downward at a 45-degree angle. We'll call this the upper right slant. Continuing clockwise around the handle, the next plane is parallel to the plane of your strings. We'll call it the side plane. The next, clockwise, is the lower right slant, and then, completely underneath the handle, is the bottom plane. We won't need to refer to the remaining planes.
Now we're almost ready to use very simple definitions of the grips. I could give a more complex description of each grip, using several points of reference on the hand and racquet, but if we just remember one characteristic common to every grip, our simple definitions will get us close enough that any variations will be within the normal range of adjustment for individual preferences. Just remember this: For each of these grips, you want your fingers angled forward toward your strings, not wrapped straight around your handle.