Depending on what you mean by a "molecule" you may be able to touch a "molecule". When you touch, for example, your desk, the molecules in your finger are "in contact" with the molecules of the desk. What are really in "contact" are the electrons in your finger with the electrons of the desk.

Electrons, along with the protons and neutrons, make up atoms. Protons and neutrons are confined to the core of the atom. More than one atom combined make up a molecule. The part of the molecule you are actually "touching" is the electrons, which are NOT confined to the nucleus (core). Do these electrons actually touch? The answer is, not really. When the electrons in your hand get VERY CLOSE to the electrons in the desk, they strongly repel each other. This is the force pushing back on your hand!

Friction is force based on interactions of the electrons moving past one another, and also microscopic roughness. Although two glass slides make appear to be smooth, there is still a friction force when they slide over one another. This is due to little bumps on both surfaces pushing against each other (their electrons are repelling one another).