Tar and resin are related in some traditional materials, but resin is usually a plant exudate while tar is a heat-made product. Together they can create sticky, water-resistant, and sometimes harder mixtures.
Resin and tar are easy to confuse because both can come from trees, both can smell strong, and both can be sticky. The key difference is production. Resin is secreted by a plant. Tar is produced by heating organic material in limited oxygen.
In practical behaviour, resin can make mixtures harder, glossier, and more adhesive, while tar can make them darker, smokier, and more flexible. Pitch, sealants, varnishes, and old maritime materials often sit somewhere in this family of resinous and tarry substances.
The interaction depends on proportions and heat history. A resin-rich mixture may become brittle as it ages. A tar-rich mixture may remain softer and smellier. Add oils and the material may spread more easily but take longer to settle.
Tar and resin work well together when a sticky, water-shedding, traditional coating or adhesive is desired. They work badly when a clean, colourless, odourless, or fully hard finish is expected.