Using worsted weight yarn (I suggest cotton) and G hook (American sizing), you can make this cheery jellyfish in about an evening. It's a relatively easy pattern - you need to know how to single crochet, increase, decrease, chain, and slip stitch. The pattern also uses a double loop start for the head, which is worked in the round as is most amigurumi.
The finished jellyfish would be a suitable baby-gift or display specimen.
The pattern will be available for direct download from Etsy in pdf format.