Step 1: Select your Image
Step 2: Fire up Inkscape!
Step 3: Add the text
Size - To size your text, click on it with the selection tool after you have finished typing what you'd like. Then use the sizing arrows in the corners to make it larger or smaller.
Color - To change the color of your text, first you must highlight it. Now just select your color from the color bar at the bottom of the screen.
Font - Similar to color, you have to highlight your text first. After that, use the drop down menu of fonts to select the one you want.