How do you cook legumes?

I personally took them out of my nutrition lineup because overall they are not something our body was meant to be taking in. There are toxins in them which you can read about on some other sites. BUT if you do want to know how to cook them I do know this part (I actually grew up eating beans because we could not afford much meat).
First you should look through the legumes for rocks/dirt or bad beans and then give them a good rinse. You would then need to soak them overnight if possible...change out the water at least once while soaking.
Then it is simply a matter of putting the legumes in a pot of water (an inch or so above the bean level) or stock/broth with some seasonings of your choice and cook them on a low simmer for a few hours. You may need to add more liquid as they cook. It is very important to fully cook them because no one likes a crunchy legume. :-)
It may be trial and error for a bit, but legumes are very simple to prepare once you get the hang of it.

if it is green, you can usually chop it up a bit, then put it in a pan on medium to med-high heat with some olive oil for a couple minutes. Near the end you can add some vegetable seasoning, pepper, garlic or some soy sauce. Styr fry instant magic goodness.

Works well for peppers, green beans, onion, broccoli, spinach.

sweet potatoes I cut then roast in the oven.

Those are my staples.

There are many kinds of legumes but I assume you’re talking about cooking dried beans? Simple.

1. Pour them on your counter and toss out any broken or discolored beans and rocks. Rinse in cold water.

2. Cover the beans with water and soak over night OR bring the beans to a boil, turn off heat and let sit for one hour.**

3. Discard soaking/cooking liquid. Cover with fresh water or stock. Add seasonings and aromatic vegetables (i.e. onion, garlic, bay leaf, herbs, ham hock, dried spices)

4. Bring to a boil. Cover. Reduce to a simmer and cook until tender (around 90 minutes, but depends on type and quantity of beans)

**You can skip this step, but it means your cooking time will double and the finished beans tend to make you gassier. Soaking them decreases the gas.

Edited to Add:
You can also toss the beans into a slow cooker. I make large quantities and freeze in smaller portions so they are ready to use.

It depends on what type of legumes you're referring to. Here's an article from the mayo clinic. Also use Google to find recipes.

http://www.mayoclinic.com/health/legumes/NU00260

These are super easy in a crock pot too. I have made split pea and navy bean soup in my crock pot and as long as you soak them overnight, it works great! Just a note: the water in my region is hard, so I was finding that I could cook the you-know-what out of the beans and they would still be crunchy. I learned I needed to buy a britta filter to get all those metals out of the tap water, made a huge difference.