The smaller stitches (if they are the same symbols as the larger one near them) are probably 1/4, 3/4, or 1/2 stitches. Usually in the directions there are instructions on how to do these smaller stitches. Check to see if this is true. If not maybe someone else on this site can help more.

How exactly do I do a 1/4, 1/2,or 3/4 stitch? :)

I love this pattern. I spent a little time looking at similar patterns by this artist. Several of the descriptions stated that 1/4 and half stitches, backstitching and French knots. Some of them did not have a description. I did not find information for this specific pattern. I am unable to explain how to do these stitches. If no one else is available to explain perhaps you can look at YouTube.

This looks like a really fun project to do.

HAVE A STITCHING GOOD WEEK-END

A half cross stitch looks like this / or if you prefer A 1/4 looks like one of the above 1/2 stitches cut in 1/2 again-sew on the fabric in the correction direction.
A 3/4 looks like one of the above 1/2 stitches with the little extra 1/4 piece going in the right direction in the middle of the 1/2 stitch. Go to www.youtube and enter "cross stitch fractional stitches". There are videos of how the stitches are made.