First of all, let me say that there are dozens, maybe thousands of techniques and products out there, so I'm just sharing the ones I use and like. It's also pure coincidence that all of the products I am sharing are by Minwax. Those are just the images I found easily.
Paste Wax -
How it's applied: Wax on, wax off. Rub the wax on with a soft/clean cloth. Allow it to dry to a haze and then buff it off.
What I like it for: Natural wood, painted surfaces, especially when I want a soft luster to the finish, not a shine. I also like that it provides a hard finish and no brush strokes.
What I don't like it for: Pieces with a lot of texture or detail. The wax gets clumped in the details and it's a mess and a pain to get out. I stick with smooth pieces.
Creative Uses: Dark Wax is a wonderful way to antique and provide protection all in one step.
One piece I used it on: My dining room table top.
Polycrylic -
How it's applied: This can be brushed or sprayed. It's water based, so it's easy to wash out of brushes and equipment.
What I like it for: I use this most on chippy pieces that need to be sealed. I can slather it on with a brush and it provides a hard, satin finish that protects my family from lead paint. I also use my paint sprayer to apply this to painted furniture when I want a clean finish that isn't distressed.
What I don't like it for: Natural wood or pieces where the brush strokes are going to show. This product leaves a lot of brush strokes, so I prefer to use it on pieces with texture (like chipping paint) or apply it with a sprayer. Also, it does dry clear in most cases, but it can slightly yellow some whites or change the color of some paints. You may want to test it on a small area before applying it to the entire piece.
Creative Uses: You can mix paint with it and use it as a glaze or extender.
One piece I used it on: My traditional hand painted dresser.
Wipe-On Poly -
How it's applied: Wipe it on with a clean, soft cloth. Lightly sand with a fine sand paper or steel wool between coats.
What I like it for: Natural wood and dark painted pieces.
What I don't like it for: Light painted pieces, because this product will really yellow paint.
One piece I used it on: The top of my vanity.
Spray Polyurethane -
How it's applied: Self-explanatory, I think! Remember to use long, even strokes and hold the paint can an even distance from the piece you're painting. It's better to apply several thin coats, instead of one thick (and drippy) one.
What I like it for: Sealing rusty metal pieces or finishing smaller pieces like accessories, chandeliers, etc.
What I don't like it for: Furniture (just a personal preference) and light painted pieces (again this product yellows.)
One piece I used it on: A rusty chicken feeder.
I'm getting ready to go to Blissdom! My flight leaves tomorrow morning and we're expecting 3-5" of snow, so please pray I get out safely and without delay.
**Please remember to follow all manufacturer's instructions for use, safety and proper disposal of these prodcuts. Also use extreme caution when sanding finishes that may contain lead paint. Please educate yourself before diving into a project!