Hello
That is such a cute pattern!
The first part is for the right front so I assume that is where you are up to. The right front is as you would wear the cardigan, not as you look a it whilst knitting, so first make sure you know which edge the sleeve needs to be worked on, sometimes I hold up my knitting in front of me to check!
For right front you will knit along right side (RS) (or public side of the fabric) from neck edge to sleeve edge. Now you are at the edge which needs new stitches to extend the sleeve.
There are two options (there are more than 2 options in reality but no need to confuse things):
You can keep your needles in this orientation with stitches on the right needle and add new stitches with a loop method, these are added to the right needle. Then turn to work the WS of the fabric a usual.
Or
You can turn the work like at the end of a row, and then add the stitches with a knit cast on or cable cast on. These are added to the left needle. Then, as you have already turned your work, you will be ready to begin the next row. Work the new stitches and directly on to the established stitches.
The second method gives a better result and is better for larger number of stitches (you will be adding 19 for one of the rows) so I would suggest this, but either will work so you can choose which you are more comfortable with.
There is a video in the drops tutorials, on your pattern page click “videos” for a list of tutorials.
Here’s the one for casting on, both methods are shown
The second method feels like adding the new stitches to the beginning of a row rather than the end, however this is often how patterns are written, it’s still the end of the row of stitches.
When you have chosen the method stick to it for the whole cardigan, don’t switch or you may get an uneven result.
For either method it’s not possible to produce the cast on stitches on every row so this will clear up that confusion
RS work from neck to sleeve edge, add stitches
WS work across to neck edge
RS Work from neck to leave, add stitches
WS work across to neck edge
And so on.
The first group of stitches is cast on 4.
The second group is cast on 4.
The third is cast on 4.
The fourth is cast on 4. (Thts 4 sts, 4 times, done)
The fifth group of stitches is cast on 19.
There is quite a lot going on in this pattern for a new knitter, lots to remember. If you are still stuck or get to another tricky bit don’t hesitate to ask again.
Hope this helps, let us know how you get on.