Now that you have a sampler, you need material to sample. Although, you can take a sample from any CD, tape, radio show, phone call, and so forth, you must be careful to not infringe upon anyone's copyrighted material. One good way to do this is to make sure that your samples are completely unrecognizable. If nobody can tell what it is... nobody can sue you!
An alternative to using material that has a copyright license is the Creative Common License. Creative Commons licensed material often can be sampled legally. Or, safest of all, be totally legit and sample your own material.
Most soft samplers actually don't record so much as they edit and play back samples. So to actually record a sample into your computer, you will need to record into a DAW. Once you have your sample saved, its time to fire up your sampler and let the fun begin.
The logical first step is going to be editing. Editing a sample can be a complex process, but for the purposes of this article, we'll only be picking a starting point and an end point.
Select a view of the waveform of your sample, and zoom in until you can see the points where each individual wave crosses form a positive to a negative value. This point, called the zero crossing point, is the exact point where you want to cut. If you cut in the middle of one of the waves (on top of the hill-shaped lines of the waveform), your sample will sound clipped.
See the illustration above, noting the position of the green bar, which indicates the starting point of the sample in each example. Remember, your ears are the best judge of whether your start and end points work or not.
If your sample is going to be played in a continuous loop, you'll generally want your loop to be a multiple of two, assuming that your time signature is 4/4. This is just a guideline for more conventional compositions. You can get some complex polyrhythms by having loops of different lengths playing together. For example, a four bar loop and a five bar loop playing simultaneously will line up every twenty beats if they are both at the same tempo. This of course is just a basic example and you can experiment with much stranger loop lengths.