What is the difference between "&" and "and" in writing?

Can I use either whenever I want to use an and?

e.g.,

I like to play and sing
I like to play & sing

We will walk and she will run.
We will walk & she will run.

Solution 1:

The choice as to which to use comes down to the degree of formality of your text, and possibly also how much space you have available (e.g. when putting together a PowerPoint slide).

In general, using & implies a much more informal tone than and.

You will never be criticized for using and, whereas you run the risk of disapproval if you use & in anything but informal notes, tweets and the like.

Solution 2:

Ampersand (&) is rare in formal written English, although in informal e-mails, texts etc. it's usually noticed.

Reference : When Can You Use It?