This game is hard to understand at first, but worth it to learn. Since no one has mentioned the easy way to have sex yet, I'll go through it. But first a small guide.
S+E is the way to drop down, and is used in many levels that appear empty at first, including the first vine area. You can drop down anywhere on certain platforms, it has nothing to do with those little metal vents.
The orange machine in the room where you respawn gives upgrades, using the orange number on your screen. You'll need 54 points (accumulated automatically) to even do anything in the game, split into 1 Strength (grabbing effectiveness, at most two upgrades needed?), 2 Endurance (time you can have sex before dying, max it), and 2 Prowess (sex bar speed, max it). Toughness is also good to get, as it increases the number of hits you can take before dying, but I still have no idea what benefit Agility and Drive give you, so it's better to save the orange points for the end.
The green number is how many elves you've seeded, once you have the stats above you can have sex by running into them and pressing E to grab. Now here's the trick to sex: HOLD the spacebar and MASH the wasd keys, it will make the green bar go up much faster than the pink opponents bar. After you get to the heart stage, fill it and press E to increase your green number. You may have to match red arrows if you're too slow, but it's still possible to seed with just the above stats.
As a bonus, once your Endurance is high enough that you don't die after sex, you can press E on the knocked out elves to have sex again, and where you press E determines doggie style or missionary, kind of like the last game.
Lastly, talk to everyone with E, and do a lot of backtracking to talk again after you finish quests, There are guides below that talk about the order of quests, so I won't bother repeating, but just make sure you talk to all the orcs and robots and monitors you find. These interaction points are often small and not exactly on the character / monitor, so it's a bit trial and error to even find out if you can interact. But basically all the monitors in your ship have a use, all the orcs except book signing orc unlock things, etc etc etc.