Aside from the many firearms available, there are also grenades, which are just as important as anything else in your arsenal. These you can carry in addition to two firearms, making you something of a walking armory. Remember: if you’re going to make it through Modern Warfare 2 alive, you’re going to need to use everything at your disposal.
Grenades are a staple of first-person shooters, especially military shooters, so it wouldn’t be complete without them. Grenades are a very effective means of taking out enemies and should be used very frequently, because you’ll find extra ammo all the time, whether it be on corpses or in weapon caches. Resupply caches also refill your grenades. Basically, don’t worry about running out. Use them freely.
Most missions start you with a whopping four frag grenades and four flash grenades. Some also give you four semtex sticky grenades.
When using frag grenades, always remember to cook them. This will give your targets less time to run away. Once you get good at it, you should be able to time throws so that the frags detonate in midair, right above a target.
Even throwing a grenade without cooking it will flush enemies out of cover. They can either run or explode. As they crawl out of their holes, you can greet them with bullets.
Flash grenades detonate on impact and blind nearby enemies. They have two major uses. When you’re pinned down by enemy fire, you can toss one in the direction the bullets are coming from and give yourself an opening to shoot back. You can also toss one into a room full of enemies, so they’re all dazed when you rush in and mow them down.
Finally, semtex is great for taking out vehicles when you don’t have an explosive weapon handy, such as a stinger or a javelin. However, they’re still grenades, so they can take out enemy infantry just as effectively as a normal frag.
Article from Gamersyndrome.com