Valence electrons are the electrons involved with chemical bonding. They are part (and sometimes all) of the outer-shell electrons, which are the electrons given after the noble gas core.
Work Step by Step
For example, $$Li: [He]2s^1$$ $[He]$ is the noble gas core. $2s^1$ refer to 1 outer-shell electron. And in this case, this outer-shell electron is also the valence electron. (For elements with atomic number of 30 or less, all outer-shell electrons are valence electrons)