Please how can one differentiate between a normal and swollen lymph node of the neck, armpit and groin. how is this treated?

See details: Normal lymph nodes are small and very difficult to feel. Swollen nodes may be significantly larger and may be tender.

Simple answer: Lymphatic system absorbs/carries things too big to go into the arteries/veins like bacteria eaten by white cells and digested food. Lymph nodes "taste" the lymph for anything bad like bacteria/viruses/cancers, etc. When it detects a problem, it alerts the immune system and your body reacts. They enlarge in response to the inflammation they create when they react. They shrink when all is well.