Tutorial by Amy Vander Vorste
We’ll start building up loops on and behind our thumb for a nice clean start to our work. There’s more than one way to do this. Here’s my favorite. I’ll be setting up for Finnish 2+2 stitch.
1. From inside of thumb to outside of thumb, wrap yarn around thumb (over nail and around) twice. The first wrap should go over the tail to lock it down.

2. Pull working yarn back and put needle under the loops on your thumb (on the inside of thumb), then pull through. This will secure the tail and give you the same setup as your stitches, with the working yarn under the thumb loop. (You want only 2 loops around your thumb at the end of this step.)

3. Pull top loop off thumb to do an Oslo Stitch (1 on thumb, 1 behind thumb).

4. Push 1 loop back behind thumb. Do one Mammen stitch (1 on thumb, 2 behind). (2 sts completed now)

5. Now you are ready for Finnish 2+2 (2 on thumb and 2 behind) in the same 2 loops behind thumb. (St number 3).

Now you’re ready to go with more Finnish 2+2 stitches in the usual manner.
This same build up start can be used when attaching a new row to an existing row of work. (Say we want to add a short row for shaping, or attach another strand to make a braid, etc.) Just put the two loops on your thumb and push one back, then pick up the loop of your stitch on the existing work and continue your new stitches as you would in the directions above.
The PDF for this can be downloaded from Google Drive.