If it turns out to be a low snow year, the creeks may be fairly calm.

In case they aren't, here are some resources that I consider worthwhile:

1. PCTA.org: Stream crossing safety while hiking and backpacking, a great intro with a primer on basic techniques. If you only read one resource, I recommend this one, because it is comprehensive and it's specific to the PCT.

2. Advice from a member of the Class of 2017, a notoriously high snow year which lead to some challenging crossings at peak melt.

3. u/AndrewSkurka's High Sierra Water Crossing Resources: blog post, Caltopo map, spreadsheet, and PDF download of the spreadsheet. More resources are linked in the blog post.

4. New Zealand's Mountain Safety Council offers an online training module about river crossing safety. There's an r/ultralight discussion about it here. Note that some of the advice from the NZMSC contradicts other resources. Further discussion can be found in reddit threads here and here.

Also, since any discussion about the Sierra seems to need a preemptive disclaimer these days:

New hikers, if you haven't already, you will likely encounter some people who seek to shut down all conversation about hiking safety as "fear mongering." We all know that 1) actual fear mongering is lame, 2) the vast majority of thruhikers complete their PCT hikes without significant physical injury, and 3) there are also a few who don't. Imo it's certainly worthwhile to put some effort into learning basic techniques to prepare yourself for obstacles that have the potential to be legitimately dangerous, without obsessing over it.