Actually, you can use a canner to cook in, but some pressure cookers are NOT suitable for canning. You need one that allows you to can at least 3 quart jars--recipes take into account the amount of time that it takes to heat the contents up, and a smaller cooker may come to pressure too quickly to make for safe canning.
The other thing a pressure canner needs is a way to control the pressure--some cookers only have one setting.
Canners will say 'pressure canner' on the packaging. Some have a weighted jiggler, some have a gauge. I have never used a gauge canner--I think they have to be monitored more closely, and the gauge needs to be tested yearly.
I use my big pressure canner (holds 7 quart jars) to can, of course, but I also use it to make stock. Some of that stock goes into jars and gets canned.
I just haven't been the same
since that house fell on my sister.