A sequence is the order things happen. Think of the sequence it takes to call someone. 

1. Hold the phone.

2. Unlock the screen if needed.

3. Dial the person's phone number.

4. Chat with the person you called!

Algorithms are important in computer programming.  An algorithm tells the computer what to do and in what sequence, or order, so that the computer will do what you want it to.  An algorithm is a process or set of rules.