This is our rhubarb plant. It is huge! It was left to it own devices for about five years and only in the last couple years we have been harvesting. I noticed that down wind there are at least another eight rhubarbs starting up so we are well on our way to being rhubarb farmers.
You want to pick the rhubarb when the bottoms are nice and red. Just pull on the stems lightly and they should break right off. I made a delicious rhubarb/strawberry crisp (from here) and then packed up the rest of my haul in freezer bags. I only froze three bags worth which didn't even make a dent in the plant but you don't want to excessively harvest as the left overs create compost for next year. If you do have a rhubarb and you don't have space for it to reproduce just wait for the seeds to sprout and cut off that stem before they start falling.
To freeze give them a wash and cut off the leafy tops where it starts to go from red to green. Some people suggest peeling the stalks but I find this way to messy so I just start chopping into 1" sections. As you chop you will notice the stringy top layer gets loosened and you can just pull it off rather than covering your entire house in rhubarb splatters! You do need to blanch your rhubarb before freezing it so drop them in some boiling water for a minute or so and then an ice bath before they go into the freezer bags. I had to do a couple batches. Suck the air out with a straw and they will stay fresh for months.
Afterwards put your cuttings back under the plant for compost and don't just dump out that nice rhubarb-y flavoured water you blanched in. Let it cool and use it to make rhubarb lemonade! It is so refreshing on a hot day!