Most types of wood require some kind of sealant to protect them from moisture and the elements. While this is particularly true for outdoor wooden furniture or buildings, indoor wooden surfaces and objects need protection, too. Depending on the environment, personal preference or necessity, there are several ways to seal a piece of wood.
If your project was a garden bench made of pressure-treated lumber, sealing its surface with oil is an easy choice. Many wood workers blend equal parts of mineral oil and linseed oil for an easy-to-apply wood sealant. Pour some on a lint-free old rag such as a scrap of denim or a worn terrycloth towel, and spread it evenly on every surface. Where possible, wipe in the direction of the wood grain. On the ends of boards use a bit extra, allowing the oil to sink into the grain ends. Wipe off any excess and let the wood dry and finish absorbing the oil mixture. If the wood dries out, recoat it. Oil lets the natural beauty and grain patterns show through. For sealing indoor wooden furniture, tung oil is an excellent choice.
Unlike oils or stains, paint seals wood by forming a protective coating on its surface. Paints for wood are either water- or oil-based, and may have a flat, semi-gloss, or hard gloss finish. Paints can be custom mixed into virtually any color imaginable and can be purchased almost anywhere. If painting bare wood has a drawback, it's that most paints require a primer coat to be applied before the finish coat can be brushed, rolled or sprayed on.
If the wood to be sealed is a deck or an outbuilding, staining the surface is another popular option. Like oils, stains are designed to both penetrate the wood and seal its surface. Stains may be clear, tinted, or solid color and may be oil- or water-based. Two popular brands of stain are Cabot and Sikkens. Both brands offer superior qualities of application and durability. Cabot and Sikkens also produce a variety of stain types and colors. They can be purchased at many home improvement stores or specialty paint stores. When applying stain outdoors, make sure the wood surface is dry and free of dirt. If possible, avoid staining in direct sunlight as the stain may dry before it has time to adequately penetrate and seal the wood. The primary advantage of stain over paint as a wood sealant, is that stain does not require a primer.
When staining indoors, work in a warm, draft-free, but well-ventilated area. Make sure the wood surfaces are smooth and free of dust, sawdust or dirt.