Crysis/Nanosuit

The Nanosuit has four basic functions: Armor, Speed, Strength, and Cloak Modes.

Armor
In Armor Mode, when you are hit, suit energy drains instead of your health. Be warned however, that when suit energy runs out, you start losing health. If you are not playing stealthily, then this mode is probably the safest to be in. If you are playing stealthily, then this is the suit mode recommended for replenishing depleted Cloak energy.

Speed
As the name suggests, this mode allows you to move around faster than normal. Walking (and swimming) speed is increased at no cost to suit energy, but sprinting in Speed Mode drains the energy bar very rapidly, so use it in short bursts. This mode also allows you to jump further, unlike Strength mode, which makes you jump higher. Melee attack speed is also increased at the cost of energy.

Strength
In Strength mode, you have increased strength. You can throw soldiers and objects further, and throwing soldiers in Strength Mode is lethal to them. Strength Mode enables you to jump higher, as opposed to Speed Mode, which makes you jump farther. Strength Mode can be used to steady your gun, which is especially useful when sniping.

Cloak
Cloak Mode generates a highly effective cloak which renders you all but invisible. Up close and in certain lighting conditions, enemies will see a shimmer of blue, and they may be alerted and start firing at you. Cloak runs out of energy rapidly when on the move, so use Armor Mode to restore energy. This is best accomplished by moving from cover to cover and switching to Armor and then back to Cloak while behind cover. Even when you are stationary, Cloak very slowly depletes, so be aware of this. Bear in mind that having a Flashlight in Cloak will probably give away your position. Also, if you fire a weapon while in Cloak Mode, all suit energy depletes, so switch to Armor before firing. Only do this if you are far away and have enough time to regain energy, or if it is just one enemy. If you think that you will be unable to get a clear shot once the enemy sees you decloak and starts moving around, then you may do this. Otherwise, you should avoid shooting in Cloak if possible.

Other functions
The Nanosuit has several other functions.

The aqualung allows you to breathe (and therefore swim) underwater for a limited amount of time. Once you take too long, you start taking damage, so limit your time submerged.
 * Aqualung

Nightvision basically amplifies light sources, allowing you to see in the dark. However, the battery life is quite pathetic, so you can only use nightvision for a short time. Be warned, though, if there is a really bright light (like a flashbang or a explosion), you will be blinded, so be careful.
 * Nightvision

Binoculars are a very useful tool that allow you to tag enemy soldiers and vehicles simply by pointing the middle crosshair at them, so that they show up on your mini-map. They are of course also useful for long-range observation and you can also hear sounds at long range, presumably with a built-in directional microphone.
 * Binoculars