AS BIOLOGY--Have I understood the lymphatic system correctly

lymph is the excess fluid that is drained from the tissue fluid, lymph nodes are swellings found at intervals along the lymphatic system, they filter bacteria and foreign materials from the lymph node, the lymph nodes contain lymphocytes which are a type of white blood cell that engulf and destroy the bacteria and foreign substances

Thank you

Close enough, except that you are filtering the lymph, not the lymph node. Lymph is essentially leaked blood plasma, but it can become contaminated because it goes much farther abroad than the blood does. The bodily function of homeostasis requires that some system control teh amount of interstitial fluid, and this is it. The lymph is eventually dumped back into the blood at one or the other subclavian veins.

The lymphatic circulation return to the blood circulation mostly through the thoracic duct (left lymphatic duct), but also the right lymphatic duct.

Lymphocyes comprise just a few types of white cell, but there are others, particularly macrophages, that are important in lymph nodes.

Lipids are absorbed from the intestine and are transported through the lymphatics as chylomicrons before entering the blood at the thoracic duct.

The lymphocytes break down all unwanted materials, whether foreign or not; (this includes cell fragments and such) otherwise, you've got it. The concept of the lymphatic system is pretty simple.