An algorithm is a set of steps which states how a task is performed. It has input data and is expected to output data. Writing a programme is creating an algorithm because you are creating steps to perform a task.
The term algorithm is used in subjects other than computer science, for example maths. It can be a set of steps to solve a mathematical problem.
Serial Algorithms- Each step or operation is carried out in a linear order
Parallel Algorithms- A number of operations are run at the same time (used in computers running parallel procesors)
There are three basic constructs which are sufficient to implement a proper algorithm.
Sequence-A linear progression where one task is performed sequentially
If-Then-Else-A choice is amde between two alternate courses of action