there are some choices:
1--do as yarn lady says.. just start
2- cast on 1 extra stitch. when you join, move first stitch cast on to same needle as last stitch cast on, and knt 2tog. (this corrects count)
3-criss cross first and last stitch
place first stitch cast on same needle as last stitch cast on.
Knit into last stitch, then into first stitch, then let both drop off needle (twist stitch)
4-knit the first (and second)stitch of round with yarn and with tail yarn, (remember --these are double yarn stitches in round two, and go into both yarn, don't knit into each loop)
there many be other 'ways' tricks but these 4 are the most common--
i sometimes use a tubular cast on, and then knit the first few 'rounds' as rows (as you do in a tubular cast on) then its much easier to join into rounds (there is more knitting) and then i sew the small seam in the tubular cast on.
you can try them all and see what works best for you.