That's rather open-ended.

For example, let's say I want to make an equation equal to 7.

3 + 4 = 7

Or:

2 * 3.5 = 7

Or:

3² - 2 = 7

You can basically start with:

x = 7

The do the same thing to both sides:

x + 2 = 9

3(x + 2) = 27

3(x + 2) - 5 = 22

If you had more specifics I could help you further.

Let's say the number is 7.

There are infinitely many equations whose only solution is the number 7.

The simplest one would be

x = 7.

Some other ones would be

2x = 14; x + 3 = 10; 21/x = 3; sqrt(x + 9) = 4;

x^2 + 49 = 14x; 3^x = 2187; and so forth.