I will let others much more experienced than me answer your question in greater detail, but in the meantime, it might help to know which DSLR you are using. There are also threads on the forum like
this one here that will help. My super simplistic instructions, based on a K-r would be the following:
1. Yes, you need to be in M mode to go fully manual.
2. On my K-r I press the [+/-] button on the top (also labeled Av) to toggle between adjusting aperture and shutter speed.
3. I use the thumbwheel to dial in the aperture I want.
4. Press that [+/-] button again to toggle over to shutter speed
5. If there is a specific shutter speed you're after, like slow on purpose to blur a waterfall or fast on purpose to stop action, use the thumbwheel to dial in that shutter speed.
6. Then watch the little meter that goes from -3 to +3 (in your example you wanted to expose for the sky so you would point at the sky while doing this)
7. Click the ISO button and dial in an ISO that centers that meter
8. Now focus on what your subject and shoot it.
Now, as I said, that's simplistic and the three things, aperture, ISO and shutter speed really work as three legs of a stool. It all depends on what you're after. In my instructions above, you could just as easily have started with an ISO and aperture that you wanted and adjust the shutter speed until the meter reads where you want. Or, if you're following along you can see this coming, you could choose an ISO and shutter speed and adjust the aperture until you get the meter reading you want. Usually, it will be a compromise between all three that give you the exact image you're after but my advice is to experiment with them a lot, Even taking 20 photos of the same subject just to see the effects of each.
That was all for the DA lens, for the M, it's different and there's plenty of threads on here about using old lenses with DSLRs. I highly recommend reading
this one. But, to get started, here's my overly simplistic instructions:
1. Set the aperture using the ring on the lens.
2. Press the green button on the top of the camera
3. Focus on your subject and shoot
4. Adjust either ISO or shutter speed and shoot again
5. Repeat step 4 until you like what you've got
Anyway, I know it's a ton of information. It was just a short time ago that I started getting a basic understanding and I have a ton to learn. But it is very fun learning and highly rewarding so keep reading and most importantly, keep shooting!