Imagine you have a secret box that you keep all your coins in. You want to make sure nobody else can open it and take your coins. So you put a lock on it. That's like a program in your computer that protects your information.
But sometimes, bad people try to break your lock and take your coins. That's like hackers trying to break into your computer and steal your information. That's why you need to make sure your lock (program) is really strong and can't be broken easily.
That's where software security assurance comes in. It means you have a team of experts who test and check your program to make sure it's really secure. It's like having some adults (experts) come check your lock to make sure it can't be broken.
So when you use your computer, you can feel safe that nobody can easily take your information because you have a strong lock (program) that was checked by experts.