Fish, this is basically designed so you don't have to actively do too much, just follow the item build. As such, pretty much all the items have passive effects.
This focuses on 3 things; range, damage per second and speed. you should be able to shoot someone from a long distance and then run away. never get near the enemy.
The exceptions are the following:
This is your escape mechanism. Activating means you can move THROUGH other units and increases move speed. Put it in a spot you can easily hotkey, and as soon as you want to escape, activate them - also use them to travel faster across the map. Later in the game, you can swap them out for a better escape mechanism if you want, that's advanced tactics.
Activate and click on an enemy hero if you want some distance from them. Works well as both an escape, and during fights to get some breathing room.
Shadow Blade/Silver Edge:
If Phase boots aren't cutting it, this can make you invisible immediately. as soon as you are in trouble, activate and walk away. However, if you are near one oftheir towers or you attack while invisible, you will become visible.
It has a special power that you can cast on yourself or allies. double press to activate on yourself and give you some passive defense, but don't worry about it otherwise.