Docking is one of the most important things to learn in Space Agency. Docking appears frequently in missions, like mission 2, 9, etc. You could make space stations, larger space crafts by docking. This is a tutorial to help you if you don't know.
Step 1: Creating the spacecraft Edit
First of all, make a space craft that contains a payload that is dockable. The payload can be anything, it depends on what you want to make. If they are carring the same payload it is suggested that if you are using two different rockets, they should both use the same rocket design because the first rocket might fail but it was the most effective design and time will be wasted attempting to recreate it. Also note that in missions, the space ships will have different "heights" so remember to make the second/third stage (or your maneuvering stage) a part that is maneuverable.
Step 2: Manouevering Edit
If your ships are already on the same orbit, just skip to step 3.
After launching both spacecrafts in space, you will need to maneuver the 1st/2nd spacecraft downwards/upwards and fire the engine until the red orbit circle touches the spacecraft you want to dock. You want to do this because even if you stop the engines, the orbit will still turn smaller/ bigger for a little bit. Try changing it if neccessary. Notice that the smaller the orbit is, the faster you go even if your velocity is the same as a spaceship in a larger orbit.
Step 3: Docking Edit
After you aligned the two spaceships together, fire the engines a little bit on the one one the back and try not to overdo it. If you didn't release the payload on the front then do it now. Carefully slow the spaceship on the back using propellant. Slowly, dock them together. If you didn't do it the first time, try again. After you docked, just press the seperate button seperate them.