You can use paint or other photo editing software to make arrows.

I used photo editing to draw the red lines around things in the screen shots below. I've found it is easier to explain things when you have actual screenshots of how it should look.

I prefer Microsoft Power Point for making my arrows as they have a wide selection of them to choose from plus you can move them around and rotate them to get them pointed exactly at what you want.

Here is a selection of arrows in Power Point

In this case here is the one I chose.

You get a cross hairs symbol (not captured with my screen shot)That you drag to make the arrow the size you want.  

Once you release the mouse your arrow is there in the default color. At this stage you can also use the dots around the arrow to expand or contract it's size and use the green dot at the top to change the rotation of the arrow. Then you can right click on the arrow and see the pop up window and select "format auto shape"

That brings up a color chart you can use to change the color of your arrow.

 Click on the color you want and then you have your arrow pointing where you want it.

Save the image to your computer and then you can upload it.