Is the app you use wysiwyg? (WhatYouSeeIsWhatYouGet)
I often use the "light meter" app on my iPhone, but I never use it for spotting etc, I use it when I am lazy and just want to get a wysiwyg-view and some values, works well enough.
What I get from metering, if you are not Ansel Adams, is that a scene is measured by a spot meter (or close to), to get the contrast range of a scene.
That is, you measure the darkest of the dark and the lightest of the light, to see how many stops are between.
I suppose one can then decide wether some tones will be outside the dynamic-range of the film, or if one is to prioritize something, over something else. (keep highlights and let shadows be black), or how to process the film thereafter. (zone-mucking about).
That is one way I guess, but unless you shoot slides, or want to AA-like control, and if you use roll-film in various light, that method is pretty moot (unless you do the same placing for all your shots, since it influence development).
Another way, is to spot-meter the important thing in your shot and decide which exposure (which zone) to place it in.
I often do portraits, and I normally put Caucasian skin at +1 stop from middle gray (zone 6) as a start, sometimes even higher.
I sometimes also try to meter highlights (like back-lit sun shining off hair and skin), to see how much range that is.
If I have a camera that has spot-metering, I will use that and simply adjust my exposure to the needle in the viewfinder.
Landscapes can be difficult, since the sky is almost always brighter than the ground, in those occasions, I may spot-meter the sky and the (important parts of the) ground, to see how many stops difference there is and how many graduated nd filters i need, to get the sky-exposure within reasonable exposure-values, compared to the ground.
Incident-metering for a (landscape) scene, where the sun is in your frame, will cause overexposure (typicaly sunsets), in those scenes, a wysiwyg-app or a reflected spot-meter (or in-camera spot) will be a better option.
I have one of these:
http://www.ebay.com/bhp/pentax-digital-spot-meter it can store several readings, and help with the final exposure.
If you have a rich uncle, you can try and get hold of a Seconic L-758, it's a meter that will cover everything you do, from studio to landscape and everything in-between, for years. It has a proper spot-meter as well.
The basics of metering, can be seen on youtube as well, there are tons of videos covering this, with practical examples, as well as studio-flash metering. ^^
Like this, think of *D* as slides, other than that, it's pretty universial: