First you need to select an alphabet you want to use. There are several types...block letters, old English, Cursive, etc.
Then chart out your letters on graph paper, allowing one empty square between each letter. Each of these squares will represent a filet block or space. You will fill in each square when charting the letters (you can either fill the whole block or just use an x which is easier).
As for knowing the amount of chains to start with, you can either work the name from bottom to top or from side to side.
I usually work them from side to side because that way I start with the same number of stitches depending on which font I use for the name.
You would chain 3 stitches for each square in the chart plus 3 stitches for the starting chain. If your first block is a space, which you would want it to be, ch 2 more, then work your 1st dc in the 5th chain from the hook.
Then follow your chart, making a block for each filled in square on your chart, and a space for each empty square.