You win by pushing every lane to the Tier 3 Towers. Once all Tier 3 Towers are destroyed, you can start breaking the Tier 4 Towers and finally the Ancient.
There's a general guide to item builds in this wiki, check here our Guides.
There are bosses in the river that drop those items. Jungle Commander will drop
Mysterious Orbs and Inner Demon will drop
Arcane Matter, below is an image of the map on their location:
Towers, specifically the 2 T4s (or 1 in 2p/3p map) near your Ancient are worth it, usually maxing 1 Tower is enough to hold up until the later wave state, but upgrading 2 Towers is fine as well. Barracks, on the other hand, are not worth it, as the lane creeps gain a lot of health but not damage, causing them to end up stalling and stacking the enemy waves.
A lot of bosses simply require teamwork or good kiting. The Blink Dagger helps with kiting and mobility, and a Spirit Vessel helps with % health boss damage and anti-heal, these 2 items can usually be bought before any troublesome boss, if any particular boss is giving you trouble, it might be worth to visit their section on the Bosses page.
Any source of damage doing above 150 per instance after the enemy defenses, and isn't from your auto attacks.
Every 4 seconds, the item rolls a 9% chance to trigger a curse, average is once every 44 seconds. When a curse is triggered, it will play a sound and stop your hero. All curses have even chances.
The curses are following:
• It can teleport you somewhere
• It can move you to a random spot
• It can drop your items
• It can deactivate itself