Hi aspirant,

Stress: It is a force per unit area. When forces pull on an object and cause its elongation, like the stretching of an elastic band, we call such stress a tensile stress. When forces cause a compression of an object, we call it a compressive stress. When an object is being squeezed from all sides, like a submarine in the depths of an ocean, we call this kind of stress or a bulk stress.

Strain: An object or medium under stress becomes deformed. The quantity that describes this deformation is called strain. Strain is given as a fractional change in either length (under tensile stress) or volume (under bulk stress) or geometry (under shear stress). Therefore, strain is a dimensionless number. Strain under a ensile stress is called tensile strain, strain under bulk stress is called bulk strain (or volume strain), and that caused by shear stress is called shear strain.

Thank You.

Stress denoted by sigma is the load per unit area or force applied per cross sectional area perpendicular to force. Stress is internal resistance of a material to distorting effect of the external force or load so these Counterforce  tend to return atoms to their normal positions. Here the total resistance developed is equals to external load.
Strain defines the deformation of an object, in strain deformation is visible and measurable quantity.