Lemon juice can be used for multitude of things. It can be part of a salad dressing. It can be added to beverages like water, soda and mixed drinks. It enhances the flavor of chicken and fish. And it can add some vitamin C to your diet.
If you just need a squeeze, then slicing off a wedge of lemon is the way to go. (Wrap what remains in plastic wrap and it should last 4 or 5 days in the refrigerator.)
If you need the juice from a whole lemon, there are a few tricks to make it easier.
Rolling the lemon on the countertop (before you slice it) helps to break down some of the fibers and the juice will flow more freely when you cut it.
You also could zap the lemon in the microwave for 10 seconds. (I did not make that one up — it really works!) This, too, will help the juice to flow.
Some TV chefs cut the lemon in half, and then cup one hand under the lemon as they squeeze the lemon with their other hand. The cupped hand is to catch the seeds. This never works for me. Maybe I have weak hands but I never seem to get enough juice this way and the seeds just go everywhere.
I like to use a juicer. You cut the lemon in half and press it down on the raised bit. The juice collects in the base. You can pick up a juicer for less than $5.