Sum function

I would like to add value daily in fix column but it's total value will show in another column automatically.

for example: first day: A1 column: 300, It's total value will be in B1 column =300 Ok.

2nd day: A1 column: 200, It's total value will be in B1 column =500 Ok.

3rd day: A1 column: 400, It's total value will be in B1 column =900 Ok.

 It will be automatically not manually. There is formula in B1 column that will mention this result.

But how it possible?