I assume that as you are in 10th grade you know that bonding between atoms is due to forces of attraction. To separate the atoms in the bond, you need to exert a force enough to overcome the attractive force between them. Now, as distance is being covered in the direction of the force separating the bonds. Hence, work is done. As work is done by the force, it means energy equal to the work done on breaking the bond was supplied to the molecule. Thus, energy is absorbed (It can be in any form; heat, light etc.).
Now, during bond formation, (taking the formation of a diatomic molecule) two atoms come close to one another due to their attractive force. Distance covered in the direction of the force is decreasing, actually having negative values according to the law of vectors. Then, as the distance covered is opposite to direction of force separating them, work is done on the force by the atoms forming the bond. The attractive force is doing work. Thus, energy is supplied by the bonding atoms to the environment providing separation force, equal to the work done. This is energy released to environment in the form of heat.
In exothermic reactions, energy released during bond formation is greater than energy absorbed during bond breaking. Concludingly, the extra energy is released in the form of thermal energy.
I think this is sufficient for you. You will learn in AS and A levels that
chemical bonds' thermodynamics is also related to kinetic energy and potential energy.
As distance between atoms increases, potential energy increases between them, and hence, work has to be done so energy is absorbed to separate them and vice versa.
Hope this will be helpful to you at your stage.