I am pretty new to blender. I have my 3D mesh and I have coordinates of a face (I mean corresponding vertices), and I don't know where it appears in the mesh. So my question is like this how can I display or even just color a face from its coordinates on a 3D mesh? I hope I was clear. I would be thankful for help.
One way you select the face by way of the co-ordinates of the constituent vertices is to make use of the 3D cursor. If the properties shelf is not visible on the right hand side of the 3D viewport, unhide it by pressing the N or clicking on the small + sign in the upper right hand corner of the viewport. Find the panel in the properties shelf window labeled 3D cursor, and if necessary, click the small triangle to the right of the label 3D cursor to open it. Enter the co-ordinates of one of the points in the entry bars to the right of the labels of the three axes, and the 3D cursor will move to the selected vertex; select the vertex. Next, enter the values for the co-ordinates of a second vertex just as you did the first in the co-ordinate slots of the 3D cursor, and navigate to the new location of the 3D cursor. Add the second vertex to the selection. You might now be able to determine which face you want from the selected points; if not, enter the co-ordinates for a third vertex, and if necessary, any other vertices for which you might have co-ordinates, and proceed just as for the first two, but in almost all cases, three vertices will be enough to give you the location of the desired face. One thing to watch out for, is that Blender keeps track of several different co-ordinate systes, global, local, normal, gimbal, and view, and you will need to make sure you are using the right co-ordinate space.
Another approach would be to take the x co-ordinates of the vertices you have, add them together, and divide by the number of vertices, to obtain the median value for the x co-ordinate, and then proceed to do the same for the y and z co-ordinates of all of the vertices. Enter the median values you calculate into the bars defining the 3D cursor location, and the cursor should in be in the desired face. Again, you will need to make sure you are using the co-ordinates relative to the correct co-ordinate space.