auto vs non-auto.
If you want to stick with auto then there's no need to play with SLRs. Its cheaper with P&S. You don't have to shoot at Manual right away, learn the basics and advantges/disadvantages of
P,A,S, modes.
First things first. On D50 (I used to have that camera), shooting above ISO400 will be noisy. Thus get out of green and get some
POWER back into your hands.
Switch camera to
P, ISO 400, pop the flash out when needed. Meter at center; matrix, as was pointed out above, might not be very accurate especially outdoors.
As you get a feel a bit more, start experimenting with A&S modes. Ideally, you should get accurate exposure for given ISO but effects will vary. Ex: ISO 400 f/5.6 at 1/200 vs iso 400 f/11 at 1/50 - exposure shouldn't change but effects will vary.
Tamron 18-200, if thats the 3.5-6.3 (I don't feel like looking up their lineup right now), again it was a lens I used to have, it is very soft at default settings, therefore on Pg 48 of your manual (or DL it from here
User's Manual - D50 - Guide to Digital Photography) Choose costume settings where you can boost up the sharpness and saturation a drop.
OF COURSE if you're shooting raw and not using Nikon's gear, then you alter that in PP. The advantage of Nikon's software is that it'll read your camera settings+raw data and will interpret them both, unlike other raw converters, will read raw data only. But that's a whole different topic and its actually I recently began experimenting with

good luck and keep on shooting.