tr = treble (triple) crochet

The triple crochet is a little taller than a double crochet. 

VIDEO INSTRUCTION

Make foundation chain 3 chains more than the number of triple crochet stitches called for. Skip first 4 chain stitches (will count as the turning chain). Yarn over hook (twice), insert hook from front to back in the center of the fifth chain from the hook. 

Yarn over, draw the yarn through the chain (4 loops on hook). 

Yarn over, draw yarn through 2 loops on hook (3 loops remain on hook). 

Yarn over, draw yarn through 2 loops on hook (2 loops remain on hook). 

Yarn over, draw through 2 loops on hook (one triple crochet complete). 

Yarn over (twice), insert hook in the center of next chain, yarn over, draw yarn through stitch, [yarn over, draw yarn through 2 loops on hook] 3 times. Repeat across to end of foundation chain. 

To begin the second row, turn your work. Chain four for the turning chain. 

Skip the first triple crochet below the turning chain. Yarn over (twice), insert hook from front to back under the top 2 loops of the next triple crochet in the row below, [yarn over, draw yarn through 2 loops on] 3 times (first triple crochet complete). Repeat this step in each triple crochet across and in the top of the turning chain at the end of the row.