For more detailed info about VS, you can go here.

Skills

Magic Missile
A magic missile is thrown at an enemy unit, causing damage. Stuns for 1.75 seconds.
Deals 100/175/250/325 damage
95/110/125/140 manacost
10 sec cd

Stun, high damage, low cd; it's really great to have. But it also has high manacost and low cast range (500). And a timed blink/waveform/etc can dodge this missile.

Wave of Terror
Shendelzare lets loose a wicked cry, terrorizing enemy units. Their armor and damage are reduced.
Reduces 2/3/4/5 armor and 5%/10%/15%/20% damage
Deals 25/50/75/100 damage which will NOT cancel potion/salve or disable kelen.
1400 cast range, 300 AoE
40 manacost
15 sec cd

A great skill to have; it decreases armor and damage of enemies, and also gives sight. Important skill to use in ganks, clashes, pushes, defends; it can also be used to scout. It's very spammable too; it only costs 40 mana and has 15 cd.

Command Aura
Increases nearby units' damage.
12%/20%/28%/36% bonus damage
900 AoE
Passive
Doesn't increase damage from raw-damage items

This skill may make VS a DPS-er, but it's an aura so it also benefits your allies (including creeps too). It's usually taken later when damage is higher.

Nether Swap
Instantaneously swaps positions with a target Hero.
600/900/1200 swap range
100/150/200 manacost
45 sec cd
Works on magic immune units
Can be improved by Aghanim's Scepter

Key skills, it can quickly isolate an enemy hero to your allies, and it can be used to save ally or yourself too. Swapping enemies might endanger yourself though, but swap is what makes VS feared the most.

Skill Build

1. Magic Missile
2. Wave of Terror
3. Magic Missile
4. Wave of Terror
5. Magic Missile
6. Nether Swap
7. Magic Missile
8. Wave of Terror
9. Wave of Terror
10. Command Aura
11. Nether Swap
12. Command Aura
13. Command Aura
14. Command Aura
15. Stats
16. Nether Swap
17. Stats
18. Stats
19. Stats
20. Stats
21. Stats
22. Stats
23. Stats
24. Stats
25. Stats

The skill build is rather simple: you get missile first because of its high damage and stun, which will help get early kills. Terror is skilled earlier than aura because terror will help better than aura early (scout+armor reduction+damage reduction > damage aura). Whenever you can take swap, skill it; it's very useful to have.

Sometimes, you may need more hp earlier. In this case, you may get stats instead of terror, but I recommend that you get stats after terror, or even aura.

Items
VS isn't item dependant, so getting high-tier items isn't her job (even though it will always be nice to have some ). You will usually get chicken and/or wards early for your team.

Early game items
Obviously you need boots but don't get it at level 1. Later it can be upgraded to any boots you want (I prefer Treads though).

It can heal you for 225 hp/mp with max charge. It's usually great to have if enemies have many casters (not to buy against Mortred/Troll/Drow/Magina/Bara etc).

Nice healing item, great if you can pick up runes frequently. It can also be borrowed to ally needing healing.

Either of these can be good for VS. Just pick what suits you the most (not a mandatory though).