Sounds like you're starting out with good sized needles and a medium weight yarn should be fine too. The yarn band will have a number in a drawing of a skein of yarn that'll give you an idea of the weight class and also a number of stitches in 4 inches that'll help classify it. Acrylic yarn is a bit less stretchy than wool so it may be slightly more difficult to work with but not a major problem.
What cast on are you using? Some are more difficult to knit into than others. Long tail is a good one to use in general for appearance and ease of cast on plus it's easy to knit the first row. I'd say, keep going even if the first row isn't perfect, even if you create holes or add stitches. The videos are very helpful and you will get it perfectly. Meanwhile, keep your hands on your needles and out of your hair!