Hi crypto Connie! To start, unfortunately you can't just run to your grocery and get some. Most, and I'm talking over 90% of all vitamin C, is made from GMO corn. You want to stay away from that. A lot of it is also made in China. You want to stay away from that. Your best bet is to go to a health food store if you're wanting to start taking it today. But, again, even at a health food store you need to be careful what you buy. All vitamin C is NOT created equal.
You want a non GMO, pure ascorbic acid or sodium ascorbate with little to no fillers. By fillers I mean preservatives or additives. Stay away from calcium ascorbate or other salt ascorbates.
I'll be doing more posts here soon on what I take and my personal protocol soon. One brand I like is Solgar, which you should be able to find in most health food stores. They make several sizes, but I buy a 1000mg capsule, which is 1 gram. I would take these through-out the day. I take personally 10 to 20 grams a day, especially during cold and flu season. Haven't had as much as the sniffles in years since I've been doing this.
Hope this helps. There is also a wealth of info at www.vitamincfoundation.org.
Take care!