If you are in a situation where you need to build a shelter, there are several different types of shelters that you can build. If you have no materials with which to construct a shelter, you should make use of any cover or protection that is available, such as a cliff overhang, a cave, a gradient, and so forth that will help shield you from wind or rain. If you are in a completely open area, sit with your back to the wind and pile any sort of equipment behind you as a windbreaker.
You can make use of any size of tree branches or even broken branches to give you some shelter from the wind. Make sure the branches are not so badly broken that they could cause bodily harm by falling. You can also make a shelter by tying a fallen branch to the base of another branch where it forks off from the trunk. Pine and fir trees make the best shelters of this sort because their leaves are the densest.
A shallow depression in the ground can give you some shelter, especially if you cover the top with branches, logs, or sticks. If it is raining, however, you may find yourself in a pool of water if you do not deflect the rain from entering your shelter.
You can use a large log or fallen tree trunk to make a shelter. Simply dig a shallow depression at the base of the trunk to give you more area. Then, lean logs, twigs, and branches up against the log to make a roof.
If you can find saplings, you can make a more permanent shelter. Just find two rows of saplings and clear the ground between them of any undergrowth, large rocks, etc. Then lash the two rows of saplings together at the top, bending them inward to form a canopy. You can make a roof by lashing together pine boughs and lashing them over the bent saplings. It would be ideal if you had a tarp with you to drape over the saplings and secure with rocks or logs at the base to keep it from blowing off.
If you are partly prepared with a poncho, groundsheet, tarp, plastic sheeting, canvas, or a large plastic garbage bag, you can quickly and easily make a shelter, especially if you also happen to have rope. The only other things you need are rocks, branches, and dry grass. You can build a shelter next to a large rock, cliff, or a barrier of trees by using the object as one side of the shelter wall. Push a branch on either side of the object into the ground and string the rope between them. Drape the handy material that you have with you over the rope. Using more rope, tie the corners to four stakes and pound the stakes into the ground, forming the material into a tent.
If you have no rope or twine, but you do have a piece of material, you can still make a good shelter. Instead of hanging a tarp over twine tied to two sticks, you can hang the tarp over a long stick suspended between the sticks. Use sticks as tent spikes or rocks to hold down the sides.
You can also make a teepee if you have long, straight sticks, twine, and a piece of material. Use three or more angled support sticks tied where they cross to make a cone. Then cover it with material, birch bark panels, or fir branches. Leave an opening at the top for ventilation. Suspending your material at its center from a sturdy tree branch can make a simpler teepee. Peg the bottom edge with stick tent stakes.
If you are in an area that has a lot of snow, you can dig out a shelter beneath the boughs of an evergreen tree. You can also dig a trench in the snow and make a roof by resting large slabs made of snow against each other at right angles. A snow cave can be dug in a drift of firm snow. After you smooth out the inside walls, make three floor levels: the highest for a fire, the next for your sleeping quarters, and the lowest to trap the cold and for storage. The lowest level is nearest to the door. Make sure you drive a hole through the roof for ventilation and to let the smoke out if you light a small fire inside your shelter. With all shelters, you should never sleep directly on cold ground. Instead, make yourself a bed out of grasses, leaves, small twigs, or whatever is handy to maintain your body heat.
These are pretty simple shelters, but first look for a shelter that is already there, such as a cave or hollow. Just be aware of any wildlife. The very best way to be assured of a shelter is to be prepared with one. An ounce of prevention is worth a pound of cure!