Yarn Selection and Gauge

Hi everyone, is there a website or link that explains how to do a gauge swatch?
Like, if I want to knit a sweater that calls for a specific type of yarn, but I’m using a different one.
I know how many stitches I need for the gauge swatch with my yarn, but I’m totally lost when it comes to how many stitches to cast on.
Thanks a lot 

Hi Diane,

just type knitting a gauge swatch into your search engine.

You’ll find several suggestions and videos that explain it well, e.g. from Schachenmayr, or ... .

I created a separate thread on this topic:
Knitting a gauge swatch: info and descriptions (No advertising)

@everyone:
There’s also a crochet gauge swatch. That makes sense. But what do you call a gauge swatch in embroidery (without the “r”)? Is there also a fabric swatch in sewing, and is there something comparable in crafts—or not really?