Here's an example of a loadout that is suitable for woodland environment while playing airsoft. A loadout is the equipment, ammunition, tools, and clothing you take with you to an airsoft skirmish.
The first thing you will need are Woodland Camo BDUs. They include the jacket and pants as well as other pieces of clothing that will be camouflaged (such as a hat, helmet, bandana, etc.). The most common is the M81 Woodland pattern which blends into grass, trees, dirt, mud and more. There is also Digital Woodland Camo, which is more modern but has the same purpose.
Next what you need are safety goggles or an airsoft/paintball mask. Make sure they are ANSI approved, or they will not withstand the impact of a high-velocity airsoft bb. The loss of an eye is a serious thing, so always wear safety equipment when shooting.
Now is a main weapon. You need an airsoft gun to be able to play (duh!). Most of the time they are rifles but can sometimes be shotguns and pistols as well, depending on personal preference. Your main weapon should be reliable, durable, accurate, and you should feel comfortable shooting it.
A secondary weapon is recommended to have, too. Some instances where you might need to use a pistol is if you are too close to someone to shoot them with your main weapon, if you run out of ammo, or if your battery dies. You can simply put your main weapon down, and grab your side arm. The most common secondary weapon is the pistol, but some people also use small machine guns (eg. UZIs) and even shotguns. They are accurate at close range and can safe you in various scenarios.
If you do chose to get a pistol as a side arm, you might want to also get a holster to hold it. There are a few types; a belt holster, a drop-leg holster, and a vest holster. They all keep your pistol safe so you can run and not worry about it falling from your pocket.
In order to shoot, you need ammunition. If you are carrying 2 guns, you might need 2 types of airsoft bbs, one for each gun. If your gun is between 180 and 250 fps and is a cheap gun (which most are), use .12g bbs. If your gun is between 300 and 350 fps, use .20g bbs. And if your gun is around 400 fps (usually snipers), use .25g bbs or higher. Never use .12g bbs on nice guns, especially AEGs because they will jam and ruin it.
Moving on to more optional gear, gloves are great for if you get shot in the hands. Paintball and biking gloves are the best because they are usually finger-less and pretty thick so you don't feel a lot of pain. But as long as they are finger-less, you will be able to handle your guns and bbs easily.
Next, you might want to get some knee pads (or pull some out if you already own some). They don't have to be expensive, tactical knee pads; regular bike or skating one work fine. They make it easier to kneel down on twigs, rocks, and bbs on the floor that are painful if you don't have them on.