Tactical nuclear weapons are mobile, shorter-ranged, and have less destructive warheads. They’re designed to be used on the front lines of a war zone, on enemy armies, and/or to create zones where it would be difficult and dangerous to move through.
Strategic nuclear weapons are often immobile (but some are mobile, e.g. in submaries), very long-ranged, and have very destructive warheads, and are designed to intimidate enemies into never attacking you, doing what you want, and/or to give you an ironic sense of safety, and hopefully dissuade anyone from using nuclear weapons on you, because you’d theoretically then use yours on them. They’re designed to be able to destroy entire cities or regions, wipe out infrastructure, and/or destroy enemy nuclear weapons, and/or cause electronics-destroying electromagnetic pulses over vast areas.