A deterministic algorithm is like a recipe that you follow step by step to make something yummy, like a cake. It is called "deterministic" because if you follow the recipe exactly, you will always end up with the same cake.
So, imagine you have a recipe that says to mix flour, sugar, eggs, and butter together, and then bake the mixture in the oven for 30 minutes at 350 degrees. If you follow those instructions exactly, you will always end up with the same cake.
Similarly, a deterministic algorithm is like a set of instructions that tell a computer what to do. If the algorithm is followed exactly, the computer will always produce the same output. Just like with the cake recipe, if you change any of the steps or ingredients, the output will be different.
This is very helpful in things like banking or cryptography, where we need to be certain that the same input will always produce the same output no matter how many times we use it. So, deterministic algorithms are used a lot in computer science to solve problems that require consistent and reliable results.