There are a few different techniques available to join new yarn to your work – one way is with a slip stitch. It is a very easy way to attach your yarn.
Step 1: Insert the hook into the specified stitch of your work and then place a slipknot on the hook.
Step 2: Draw the slipknot through the stitch and chain-1.
Step 3: Continue with the pattern instructions, working the first stitch in the same stitch as the join (unless the pattern states otherwise).
Step 4: This photo shows how the stitch looks followed by 4-single crochet stitches.