This is a simple heart for filet crochet, that I created for the purposes of explaining filet and for practice. I like to think of filet crochet as painting with crochet thread. By painting, I mean just filling in the squares to create your shape. You don't have to limit yourself to neutral thread colors since there are so many colors of crochet thread/yarn out on the market. You can make detailed pictures by crocheting(painting) with thread or yarn. Thread is used for this pattern which is why the size is smaller. You can practice with yarn. It will just be larger and a good way to practice if you are not comfortable with thread.
The multiple is 3 + 5. This just simply means that 3 chains are required to complete a square. I have 30 squares on my chart. I take 30 x 3 = 90 + 5 = 95. It will take 95 chains to start. Remember, I need 5 additional chains at the beginning to represent my beginning double crochet, chain 2. After that you follow the chart.
It is important to mark your rows off to keep track of what you have done. I take a document protector and place it over the page in the crochet book. I use a grease pencil to mark off the rows. That way it protects my pages so I can use them again. If I make a mistake, I take a tissue, wipe the grease pencil off my document protector and start over. This leaves the good rows still covered by my grease pencil and helps keep track of where I am in my project.