When we say that a person is respectable, we mean that they behave in a socially acceptable way. They work, they keep themselves and their house clean, they are morally good, they obey the laws, etc.

When we say that a thing is respectable, we mean that it is good or satisfactory. A respectable salary is a good salary for that job, but not an unusually high one for that job. Satisfactory grades are good but probably not very high.

When we say that someone is respected, we mean that many people admire them for their good work or achievements.