Video Tutorial

Row 1: 12 double crochet magic ring
Row 2: (between the stitches, not on the stitcch) *1 increase, chain 3, skip 2 stitches*. Repeat from * to * to the end
Row 3: *1 increase (on the stitch), 1 double crochet (between the following stitches), chain 3*. Repeat to the end of the row having 6 groups of stitches
Row 4: *1 increase (on the stitch), 2 double crochet (between the following stitches), chain 3*. Repeat to the end of the row
Row 5: *1 increase (on the stitch), 1 increase (between the following stitches) 2 double crochet (between the following stitches), chain 3*. Repeat to the end of the row
Row 6: *1 increase (on the stitch), 5 double crochet (between the following stitches), chain 3*. Repeat to the end of the row
Row 7: *1 increase (on the stitch), double crochet (between the following stitches) to 4 spaces before the end, 1 increase(between the following stitches), double crochet to the end of the group(between the following stitches), chain 3* Repeat to the end of the row
Row 8: *1 increase (on the stitch), double crochet to the end of the group (between the following stitches), chain 3*. Repeat to the end of the row
Repeat rows 7 and 8 to have the distance between both armholes
Row of the armholes: Make the first increase of the first group. Count the number of stitches you have to the end of the group. Make the same number of chains as stitches you have (for example, if you have 11 stitches, make chain 11). Finish the first group with an increase between the 2 last stitches of the group. Make the second group normally. Repeat the first group making the chains. Finish the 3 last groups normally
To the end of the jacket, repeat rows 7 and 8 to have the size needed

Sleeves
Make 1 double crochet on each stitch making a round around the armhole (make 2 stitches on each corner to complete the round)
Row 1-2: 1 double crochet around
Row 3: 1 decreases, 1 double crochet to the end of the row
Repeat rows 1-3 to have the size of the sleeve that you need.
Repeat the same with the other sleeve