Ward.
Don't feed.
Good to go.
EDIT: Also, here's some things you might want to know.
Carries: (Usually) Need gold to do well. Tend to be agility-based, though there are STR and INT based carries. They become very powerful late game with lots of items, and "carry" the team. Some easy/fun ones to try are Juggernaut, Luna, Faceless Void, Phantom Assassin. You MUST be able to consistently last hit and not die very often if you want to carry. Otherwise, you're just a burden on your team.
Supports: Do not need gold; they do thrive on XP though. The reason for this is they tend to have lower damage and attack speed, but have very good abilities. You buy support items (wards, courier, mekanism, pipe of insight), and (tend to) build other castery items (aghanism scepter, which upgrades your ultimate; Eul's Scepter of Divinity; Rod of Atos; etc.). You do not need gold or kills to be a good support; you want to get few deaths (though doesn't matter as much if you die as a support, just don't feed), and lots of assists. Try to keep up XP. Good supports to try out are Omniknight, Bane(ish, can be hard), Ogre Magi (very easy), Warlock, Vengeful Spirit (you will die alot), Lich, and Lion (This one is very fun IMO). Supports need to be able to land their abilities.
Other: Anything that isn't a support or carry; there are also semi-carries. This category is more hero-dependent on what to do. Examples of this are Bristleback (semi-carry), Axe, Tiny (semi-carry), Abaddon (Support/Carry).
These categories are very broad terms, so don't judge everything on them. Heroes can also be defined as other things outside of what they are (for example, Earthshaker is both a support and an initator), but make sure you know how to play before trying any carries. Type "Dota heroes" into google and click on the first link for a nice list of heroes that you can sort by what they are.
Last hitting: Be the last thing to hit a creep before it dies. Can be hard to get the hang of it, but just do NOT auto-attack, whatever you do. Autoattacking in lane (not late-game) makes it hard to last-hit and also pushes your lane. Pushing your lane is bad. You want to last hit because last hits give you gold. Do not last hit if you are a support and there is a carry in your lane.
Denies: Be the last thing to hit your own creep before it dies. Can only hit your own creeps when life < 50%. You want to do this because it prevents enemy heroes from getting gold and also reduces the amount of XP they get from the creep. Do this as much as you can if you are a support.
Harassing: Hitting/Using abilities on enemy heroes while in the laning phase. Do this as much as you can. Focus more on last hits if you are a carry, though.
Ganking: Going to other lanes in order to kill enemy heroes. I recommend you do not go mid (as in, starting in the middle lane) as they tend to be the gankers (not strictly true in all situations, but generally, in low-level games, the Mid will be ganking).
Lane Setup: So, the longest lane is known as the "safe lane", and the shortest lane is known as the "hard lane". Mid-lane is known as mid. For Radiant (the bottom left), safe lane is bottom, hard lane is top. For Dire, safe lane is top, hard lane is bottom. Safe lane tends to be safer. The normal setup is to have 1-2 heroes in the "hard lane" (1 carry and 1 support OR 1 offlaner; more complex stuff though. Don't recommend offlaning when starting to learn), 1 hero "Mid" (There are certain heroes that are good mid; Pudge, Viper, Zeus, Outworld Devourer, Skywrath Mage are all examples. Don't go mid when you are new), and 2 heroes bottom (1 carry and 1 support. I recommend trying support or carry in the safe-lane). There can also be Junglers. Junglers are heroes that roam around your own jungle, killing neutral creeps. Examples of this are Lycan, Ursa, Chen, Nature's Profit (in low-level games), Enchantress. I do not recommend trying to jungle when you first start out.
Feeding: Dying repetitively. Don't do it.
ALSO: At the top left you'll see a small book; click on this. You'll see a thing for guides, look at the guides and click on (6.82) build for your hero. It recommends what items and abilities you should get, follow it to the letter when first starting out.
If you have any questions, ask away.
