solve is exact. nsolve is numeric from a guess.

Goal

Solve x^2-5x+6=0 and cos(x)=x.

import sympy as sp
x = sp.symbols('x')
print(sp.solve(sp.Eq(x ** 2 - 5 * x + 6, 0), x))

import sympy as sp
x = sp.symbols('x')
print(sp.solve(2 * x + 3, x))

import sympy as sp
x = sp.symbols('x')
print(sp.nsolve(sp.cos(x) - x, x, 0.5))

import sympy as sp
x, y = sp.symbols('x y')
print(sp.solve([x + y - 3, x - y - 1], [x, y]))