Question

how could you bets define exothermic and endothermic reactions

Answer 1

release of energy is exothermic, that means if you combine something like CaCl\(_2\) with water and stirr it you will see that the beaker gets hotter, it's reeleaseing energy into its enviroment, and can also be explosive!
on the other hand, an endothermic reaction means that it' absorbs energy, so, maybe something like ammonium nitrate mixed in water you may notice that the beaker will get colder, this is an endothermic reaction. Also, endothermic reactions can't occur spontaneously, while exothermic rxns can occur spontaneously.