Early game starting items are the quickest way to tell if a player is bad at dota or bad at math(not necessarily both).
When you start a game where you pick your hero, you start with 603 gold. When you start a game where you random your hero, you start with 853 gold.
DO BUY:• Ironwood Branches(53 gold, +1 str, +1 agi, +1 int)

• Gauntlets of Strength(150 gold, +3 str)

• Slippers of Agility(150 gold, +3 agi)

• Mantles of Intelligence(150 gold, +3 int)

• Ancient Tango of Essifation(125 gold, 4 per stack, Eat a tree to restore 115 hp over 16 seconds(7.18 hp/sec regen)

• Healing Salve(125 gold, heals 400 hp over 10 seconds, if you receive damage it is interrupted)

• Lesser Clarity Potion(50 gold, regens 100 mana over 30 seconds, if you receive damage it is interrupted)

• Ring of Protection(175 gold, +2 armor, upgrades to either Tranquil Boots or Ring of Basilius at side lane!)

• Magic Stick(200 gold, If enemy casts a spell by you, +1 charge. Click to release charges, heal 15 hp/15 mp per charge stored. Stores up to 10 charges).

• Animal Courier(150 gold. Drop to have movable unit that can carry items from base to your team. EVERY TEAM SHOULD HAVE A COURIER AT GAME START)

• Observer Wards(150 gold. Gives vision where placed for 6 minutes. Buy if you want to try hard in a noob game, which you do if your team can execute teamwork well! I will not talk about wards later, but there are lots of good guides)
GENERALLY DO NOT BUY:• Boots(450 gold, +50 movement speed)

• Bottle(650 gold, 3 charges of 135 hp/70 mp regen, bottle fills at base can store rune and refill with rune pickup)

• ENTIRE Wraith Band(485 gold, +6 agi, +3 str, +3 int, +3 damage)

• ENTIRE Null Talisman(470 gold, +6 int, +3 str, +3 agi, +3 damage)

• ENTIRE Bracer(525 gold, +6 str, +3 agi, +3 int, +3 damage)

• NOTHING, SAVING FOR RING OF HEALTH LOL(875 gold, +5 hp/sec regen)

As you can see, it is recommended that you purchase cheap items that give you stats, and cheap items which give you regen.
Stats give you last hitting potential(you can last hit creeps BEFORE your enemies can because you do more damage, stats give you more hp to save your life when running away, and stats give you more mp to cast spells to save lives or take lives; KILL THEM)
You may be confused why I wrote no Bracer/Null Talisman/Wraith Band. The only reason to make those items is to free up space. In DotA you can only carry 6 items. Early game, you have 6 slots, and no good items. Therefore, why would you purchase a Wraith Band(1 slot, 485 gold, +6 agi, +3 str, +3 int, +3 damage) when you could buy 3 Ironwood Branches, 1 Slipper of Agility(4 slots, 309 gold, +6 agi, +3 str, +3 int)? Later you can make those branches into a wand(GREAAAATTT item for most heroes), or sell the branches back for half of the gold(26 woot woot!). That 176 gold difference between a wraith band and the brach/slipper combo gives you extra money to buy regen. That regen is used when you are ALMOST KILLED and lets you stay in lane longer for more exp.
The easiest way to destroy noobs in lane is harassing them out of lane. Often noobs only purchase 1 set of Tangos because they spent all their money on a “big” item like Boots, Bottle, or a Wraith Band. When you see this, HARASS THEM OUT OF THE LANE. They will have to leave because YOU came to lane with 2 times as much regen. Congratulations, you now have lane control because they left to heal, and you get a level advantage.
So remember, buy stats and regen in lane. Those keep you in the lane to farm, gain exp, and put you into a favorable position later in the game. DO NOT BUY BOOTS FIRST.
Item Priority immediately AFTER your starting item builds is one of these items:
• Boots(450 gold, +50 movement speed)

• Bottle(650 gold, 3 charges of 135 hp/70 mp regen, bottle fills at base can store rune and refill with rune pickup)

• Ring of Health(875 gold, +5 hp/sec regen)

• Magic Wand(200 gold, +3 stats If enemy casts a spell by you, +1 charge. Click to release charges, heal 15 hp/15 mp per charge stored. Stores up to 15 charges).

• Flying Courier(220 gold. Upgrades Courier to 150 hp with speed burst and flying. A support should upgrade the courier).

You might be confused because a lot of these are the same as what I just told you NOT to get with your starting gold. It's common for new players to assume the "final destination" is worth rushing for, but it you pick up smart starting items and then transition into your early core items such as bottle/boots, you will have a smoother ride, on average.
If you want a recap or a summary of starting item builds, watch this video:
It won't be pro level play, of course, but as a newbie? Definitely a hero you can do decent with early on.
Just press stop and the animation cancels, doing nothing.