How to put freon in a nissan altima

Your Nissan uses R134, not R12 which is freon. Freon is unavailable these days, even older cars that used to use it must be converted, but all that is moot because that's not what you need anyway. You can buy a kit that comes with instructions, they set it up so you can't pump from the compressor in to the can and blow yourself to smitheereens. It goes on the low pressure side of the line to the compressor

OK I didn't read the bottom, you already have the R134. sorry 'bout that for my not paying attention and only looking at the title of your question. But the connection is still on the low pressure hose.

Can I come and get that now