Put a comma before the and because there is an independent subject and verb after the and.
...I was driving northbound on Madison, and I turned left onto Rourke.
...Rachel went to the hospital, and she spoke with the doctor.
No comma before the and in these sentences because there is not an independent subject and verb after the and.
...I was driving northbound on Madison and turned left onto Rourke.
...She went to the hospital and spoke with the doctor.
If the and is left out, there needs to be a comma to separate the verbs so that they do not run together. This is called the "comma of omission" and is inserted when two elements in compound construction need to be separated because there is no conjunction between them.
...I was driving northbound on Madison, turned left onto Rourke.
...She went to the hospital, spoke with the doctor.
This rule is used for any compound combination where the conjunction is omitted.
...went with Mr. Ray and Mr. Norman...
...went with Mr. Ray, Mr. Norman...
...saw her on Friday and Saturday...
...saw her on Friday, Saturday...
Happy punctuating!
Margie