Use a pressure canner for green beans; they are a low-acid food and cannot be safely canned in a boiling-water canner
Wash jars, lids, and bands
Wash and trim green beans
Cut beans to jar height if needed
Pack beans into hot jars, leaving 1 inch of headspace
Add salt if desired, using canning salt
Fill jars with boiling water, keeping 1 inch of headspace
Remove air bubbles
Wipe jar rims clean
Place lids on jars and screw bands fingertip-tight
Process jars in a pressure canner at the correct pressure for your altitude and canner type
Allow pressure to return to zero naturally before opening the canner
Remove jars and let them cool undisturbed for 12 to 24 hours
Check seals after cooling
Remove bands, label jars, and store in a cool, dark place