When doing woodwork or working with hazardous fumes, you should always wear a mask. Most people think an inexpensive dust mask will protect their lungs, but that's not the case. Think about the kind of work you'll be doing and choose the protection that's right for the job.
Disposable masks are inexpensive.
They're best suited for light wood sanding and finishing jobs where you're dealing with nontoxic dust particles. A nice thick mask made of woven materials like paper or recycled cotton is excellent for dusty conditions. It has two straps and an adjustable nosepiece. You can get a real good fit with this one, and it's good for work in most all dusty situations. Use this once, then throw it away.