If you are submitting your app for security review ,you will need to enforce CRUD-FLS for all your DML and SOQL since apex does not enforce it automatically.
There is a blog post link below that shows how to enforce CRUD FLS
You will use describe call to find the access level and prevent the DML if user does not have sufficient access .
If your project has lots of apex then you may want to use some library that's build to specifically handle heavy lifting of checking CRUD/FLS .The project is open source here
The project has utility methods to wrap the DML to perform checking of access before any DML .
Note that if you are not building a managed package and instead customizing single org and if there is no strict requirements around security enforcement you may skip these checlmarks warnings