SQL UPDATE Statement and Best Practices

This video includes two variations of a simple SQL update statement. One variation has just the table name and two columns being updated whereas the second variation specifies the database, the owner, and the table to make a more complete declaration. Update statements are critical to change existing data.

[hasanmougharbel]

Hey my friend, blessed to discover your channel.
I have only a simple enquiry as a newbie sql learner.
What is the main difference between alter and update in terms of their application in sql?
Thanks for taking time on this..