SR only deals with situations in which gravity is not present or can be neglected; in such situations, spacetime is flat, or can be approximated as being flat.

GR deals with situations in which gravity is present and cannot be neglected, and spacetime is curved.

And, if OP is wondering about why the names are what they are....

The case in which gravity is not present or can be neglected is a special case (curvature is zero) of the more general theory that works for all values (zero or non-zero) of the curvature.

Although not directly related to the question, OP may also be interested in the relative difficulty of the math behind the two theories.

High school algebra can get you to a decent understanding of SR: derivation of Lorentz transforms from Einstein's postulates; calculation of spacetime intervals and proper time along the worldlines of objects moving at constant relative velocities; able to explain the elementary "paradoxes" such as pole-barn, bug-rivet; the various approaches to the twin paradox.

GR requires multi-variable calculus, differential geometry, tensor calculus, solving some of the most challenging non-linear partial differential equations you'll ever encounter. There's close to a decade of high school and college math between SR and GR.