A slip stitch (sl st) is the shortest and flattest of all the crochet stitches.
Slip stitches can be used to crochet a whole piece of fabric and would usually be worked into the 'back loop' to do this. It may also be used to move your yarn across a group of crocheted stitches, adding very little height, but generally, it is used to join one stitch to another. A crochet slip stitch is technically a utility stitch.
1 Begin with a slipknot on your hook. Make a chain length of 5 chains, insert your hook into the first chain (my tapestry needle is showing you the first chain),
2 With your yarn hand, wrap the working end of the yarn over the hook from back to front over the top (yo), and with your hook hand, turn the hook towards you and draw the yarn through the chain stitch and then through the loop on the hook.
Slip stitch complete.
OR
If you do not want to make a circle, you can practice on a straight row as follows:
3 Make a length of 6 chain stitches (not including the loop on the hook) . With your yarn hand, hold onto the chain length and insert your hook into the 2nd chain from your hook (where I am showing you with my tapestry needle),
4 With the working end of the yarn over the hook from back to front over the top (yo), and with your hook hand, turn the hook towards you and draw the yarn through the chain stitch and then through the loop on the hook.
Slip stitch complete.
5 Carry on making slip stitches into each chain stitch along to the end as follows:
*Insert hook into next chain, yarn over and draw the yarn through the chain stitch and then through the loop on the hook; repeat from * to the end.
Slip stitch complete.
Also you might like to see How to crochet a straight Granny square HERE
And How to crochet a straight Border HERE