*bear in mind I only see planes at 1 to 5 miles alt for the most part
I assume the engine is spun by an electric motor somehow and when a certain rpm is reached fuel and some kind of spark is induced to start the combustion process. Once the engine is up and running, I've been at airports to know that the engine runs and prop doesnt. So, how or what transfers the engine power to the prop and is there a clutch of some sort to engage the props?
A turboprop engine is basically a jet engine with a prop attached to it. There are two types -- one in which the prop is driven through an output shaft and gearbox, and what's called a free turbine, in which the prop is driven by the combustion gases in the engine instead of by an output shaft. The best known free turbine is the Pratt and Whitney PT-6, and this is the one you may have seen where the engine and prop can turn independently of one another.
A PT-6 has glow plugs (sort of like a diesel engine) to ignite the fuel. Most other turbine engines use an ignitor plug, which is basically a really high voltage spark plug. The ignition can be turned off once the engine is running, as the combustion process is self sustaining once the engine is running.
On the smaller HP turboprops the starter is usually electric and spins the engine up to a minimum speed at which the fuel can be added without the engine frying itself. The ignition is enabled at that time also and once the generation of hot, high speed gas is underway, the RPM begins to increase rapidly. Once the RPM reaches a predetermined value, usually around 35% of total RPM possible, a reverse current relay kicks in and the DC starter becomes a DC generator, hence the moniker "starter/generator" for these units. There are certain advantages to this arrangement, this greatest being the elimination of one rather heavy engine accessory in favor of a dual purpose unit.
However, some larger T-props have AC generators to produce 400 Hertz (Cycle for the unwonkish) 115 Volt, three phase, Alternating Current. (Your car's alternator produces 12 to 14 Volt single phase alternating current but that is immediately rectified into DC so that the term "alternator" is appropriate for a system different from the kind used in large aircraft, some of which use AC current. Why use AC? For the same reason that most electric models fly better and longer on brushless AC motors rather than brushed DC motors; lighter overall weight and more power vs. weight.)
The larger T-props use either an onboard APU, ground Air Turbine cart, or terminal jetway air sources to set the engine in motion for starting. If an engine is already running, i.e., started with a one-shot bank of HP air bottles or large low pressure air tank or even just left running during a stopover, a crossbleed start using air generated by the running engine is usually possible.
All turboprops run their power through a gearbox to bring the very high speed of the compressor/turbine shafts (12,000 RPM or more) down to an RPM more suitable for spinning the prop.
The smaller Pratt & Whitney Canada PT-6 series of engines uses an air coupling that works much like an automobile's torque converter to transfer power from the turbine to the prop but air rather than transmission fluid is the transfer medium.
Turboprops on larger aircraft are often geared directly to the turbine/compressor shaft(s) and depend on the engine coming up to speed with the prop in flat pitch to minimize prop drag and allow the selected air source to spin the engine up to start speed and beyond to a self-sustainable speed.