Finally managed to launch something into space...
but now how do I go back? 2100 Km and still climbing. I only wanted to orbit below 100 km!!!
I guess I should have saved some fuel to eventually come back.
I'm not sure, but I don't think leaving the planet's gravity well is simulated in this yet, so you will,
eventually come down. I'm not going to try to give you a time frame on that though, it could be hours, or days, depending upon how fast you're still going at that height.
As someone said before, a low orbit requires roughly 2200 m/s of horizontal velocity. So, once you're sure you'll be high enough to get out of the atmosphere (very hard to judge), start pitching nose towards the horizon to give yourself plenty of horizontal velocity. Don't burn all your fuel that way though. Once you get to about 2200, you should cut thrust. At this point, your velocity should be slowly decreasing. This is because you're still ascending slightly. Once your vertical speed reaches zero, your velocity should start increasing again. At this point, point your nose in the direction of movement, or slightly above it, and give yourself some more thrust. It doesn't take a whole lot, but this will ensure that your periapsis (the lowest point of your orbit) is clear of the atmosphere. It's very hard to judge this last burn, just based on the info given to you. However, I'd suggest leaving at LEAST 1/4 to 1/2 of a liquid fuel tank for deorbiting if you're planning on trying to get back.
I've managed this once, with a design that's slightly odd and unreliable. It required a layer of solid boosters on the bottom, which fired, but didn't lift the rocket from the pad. I'd seperate those, and then ignite the liquid rockets, which would cause the lower solid ones to explode, occasionally taking one of the liquid ones with them, but usually just giving the whole thing enough of a bump off the pad to lift off.