To take a full backup and differential backup of all databases Can anyone help me with a script to take a full or complete backup of all databases once in a week and to take differential backups daily. ?
You should look at Ola Hallengren's scripts 

https://ola.hallengren.com/ 

The FAQ has examples on using these scripts with SQL Express.

https://ola.hallengren.com/frequently-asked-questions.html