How to Crochet a Celtic Square
A Celtic square is an attractive crochet project that's less complicated than it looks. To make one, you'll need to make a chain of 28 stitches and then slip the ends together to make a loop. Chain 3 next to the slip stitch, then do a series of double crochets to make the corners and edges of the first square. Next, make 2 more squares using the same technique, but don't close them off. You'll be weaving these around your first square to make a knotted pattern.
Grab the yarn of your choice. Now do a slip knot. One way to do this is to fold the yarn and hold it between your thumb and index finger. Twist the string to form a loop, and pull the rest of the yarn through the loop. Then insert your crochet hook into the loop left. Chain 28. To do a chain stitch , yarn over once to get two loops on your hook. Pull the first loop through the second loop to finish the chain stitch. Repeat this 27 more times before moving on to the next step. Slip stitch into the first chain. To do this, insert your hook into the first chain. Yarn over while your hook is still in the chain.  Pull the loop you thread over through the first chain and the other loop. You should see a circle/square like shape forming now. Chain 3. After the slip stitch, chain 3. This is to prepare for the double crochet that you will be doing afterwards. Double crochet into the next stitch. Start the double crochet by yarning over once. Insert your hook into the next stitch, and yarn over again with your hook in the stitch this time. Pull all the loops through the stitch. You should now have 3 loops on your hook. Yarn over again and pull through two loops. Yarn over one last time and pull through the remaining loops. This stitch can also be called treble crochet in UK. Do 4 double crochets in the next stitch. This reason to do four is because this is a corner, and you need four to help you turn and change direction. Double crochet in each of the next six chain stitches. There should be only one in each stitch now, as this is not at a corner. Do 4 double crochets in the next stitch, again. This is a corner once more, which is why there are four double crochets crowded in one stitch. Repeat. Double crochet in each of the next six chain stitches, do a corner; repeat this until you get to the first double crochet made. Slip stitch into the 3rd chain of the first double crochet. This 3rd chain was formed when you chained 3; so slip stitch into it. Now, you should be able to see the square shape clearly. Finish off the square. Do a chain stitch, and pull tightly to form it into a knot. Cut the thread, and weave in the ends. Get another yarn that is a different color from the center square. Do a slip knot, and chain 36. Double crochet in the fourth chain from the hook. Then do another double crochet in the stitch after. Do a corner. This is the same as for the center square: four double crochets. Double crochet in each of the next 16 chains. Be sure to count the exact number. If you are having trouble keeping track, try counting out loud. Do a corner again.  Double crochet in each of the next 14 chains. You can now finish it off. This time, however, do not weave in the ends. You will need them for closing the oval later. Repeat the steps to make a second unclosed-oval. This one, however, should be made of yarn that is a different color from both the center square's and the other oval. Grab the center square and one of the unclosed-ovals. Take one end of the unclosed-oval. Weave the end over one side of the square and under the opposite side. Now take the other end and do the same, except opposite: weave the end under the first side and over the opposite side. Take the loose string. Weave it back and forth between the two ends. This will close the previously unclosed-oval. Then weave the remaining part of the string in. Grab the other oval (that is still separate from the center square). Like before, take one end of it. This time, though, weave the end over one of the two sides of the square that has not been woven by yet, under one side of the other oval, over the other side of the other oval, and under the opposite side of the square. Then take the other end and reverse the process: under, over, under, over. Close the unclosed-oval as you did for the other oval. Your Celtic square is now finished! 
Grab the yarn of your choice. Chain 28. Slip stitch into the first chain. Chain 3. Double crochet into the next stitch. Do 4 double crochets in the next stitch. Double crochet in each of the next six chain stitches. Do 4 double crochets in the next stitch, again. Repeat. Slip stitch into the 3rd chain of the first double crochet. Finish off the square. Get another yarn that is a different color from the center square. Double crochet in the fourth chain from the hook. Do a corner. Double crochet in each of the next 16 chains. Do a corner again. Double crochet in each of the next 14 chains. Repeat the steps to make a second unclosed-oval. Grab the center square and one of the unclosed-ovals. Take the loose string. Grab the other oval (that is still separate from the center square). Close the unclosed-oval as you did for the other oval. 