Templar Assassin/Lanaya is my favourite hero from Dota 2.

She's a real nightmare when she gets some kills early game and her abilities are pretty good for ganks, rune and map-control overall.

I always build her up with Phase Boots and Yasha early-game for extra mobility, damage and attack-speed, then Desolator, a must-buy item for TA because her armor reduction pwns, and then you could get a Crystallis/Daedalus, a BKB or a Blink Dagger.

BKB and Blink Dagger are very important situational items for TA, because stuns and disables can ruin her, so be keen when building her, always watch for counterpicks because she can be useless vs Venomancer/Viper or any hero who counters your Refraction.

I will describe why and when would you pick each item, and how to use her abilities.

Also, here's a video in my Youtube Channel in which you can see her damage output with some of the items I recommend and how she helps a lot in ganks: https://www.youtube.com/watch?v=ep6vnYICe6k

Have fun! Feel free to ask me any questions!