Re: How to level up quickly?
early game you want to stay in your lane as long as possible (as in don't go back to fountain) this can be done by getting Regen items (ring, tangos, flasks, bottle) or stats such as branches to boost ur survivability, also stay within experience range of creeps dying
nearing the start of mid game (let's say after level 8)... or earlier, if your friends are ganking and you are close by, help them, ganking and killing heroes (or staying close to experience range) will help you level up along side your friends
besides that, just remember not to roam around doing nothing (trying to gank and fail, running back and forth from fountain, or dying a lot) these are all ways to slow down your experience level
play smart, stay safe, be aggressive only to bait, initiate ganks, or follow up ganks depending on your hero, in the heat of battle don't run away if no one is hitting you, attack (but when in trouble run in different directions from teammates, use juke spots, or run to heroes coming to save u)
as for gold, concentrate on last hit since you are a beginner, most likely you play in games where denies don't do that much (but always good to practice to deny) and don't die (call missings heroes, listen to your team, check minimap, don't wander off too far, if you push far and expect a gank, think of where the enemy may come from and don't walk that way, carry a tp, use juke spots)
remember to harass enemy back if you have the mana (and you don't need to save it for a special occasion), and if you are range, try to harass back those enemies who walk up close to you in order to harass you (keeping enemies hp low as well can reduce their aggressiveness (so they don't tower dive to kill you, or they stop walking up to hit u as much and so u can stay in lane longer)