Step-by-step explanation:
The Basic Steps of Endocytosis
The plasma membrane folds inward (invaginates) forming a cavity that fills with extracellular fluid, dissolved molecules, food particles, foreign matter, pathogens, or other substances.
The plasma membrane folds back on itself until the ends of the in-folded membrane meet. This traps the fluid inside the vesicle. In some cells, long channels also form extending from the membrane deep into the cytoplasm.
The vesicle is pinched off from the membrane as the ends of the in-folded membrane fuse together. The internalized vesicle is then processed by the cell.