To join plain knitting (stockinette stitch),

• Attach the yarn at the right hand edge of the upper piece.
• Put the needle down through the first stitch on the lower piece (knit-wise) and bring it up through the next stitch (purl-wise). Draw up the yarn.
• Put the needle down through the first stitch on the upper piece and bring it up through the next stitch.
• Put the needle down through the same stitch as before on the lower piece (the one the needle came up through before) and bring it up through the next stitch.

To join garter stitch , combine these two methods. Place the two pieces so the knit row on the top and the purl row on the bottom.

• Attach the yarn at the right hand edge of the upper piece.
• Put the needle down through the first stitch on the lower piece and bring it up through the next stitch Draw up the yarn.
• Bring the needle up through the first stitch on the upper piece and put it down through the next stitch.

Repeat these steps until all the stitches are joined.

The needle's path is up-down on the upper piece, and down-up on the lower piece.

The needle is inserted knit-wise. Up means purl-wise.

You are purling the upper row of stitches and knitting the lower row.

Do not draw up the yarn too tightly.

Joining ribbing is similar, go down-up for knitted stitches and up-down for purl stitches.