Hi,
Below is the difference;
As you know the client is highest level in SAP hence the setting or masters are define in three.
Client Level, Company code level, and Area Specific. Like Sales & Distribution and Purchasing.
In General
Client Level is called the things which is depended on client or Client will share the information or required information for the company codes Exam : Vendor Master, Customer Master, Company details
These can be able to view every one at client level ( Credential and Authorization for Company codeis matters)
Company Code: this we can say the data which is dependent on company level like; pay terms, payment method, bank data, reconciliation accounts etc. here include co. code related configuration as well.
Chart of Accounts : Here we are customizing the setting like COA under COA Accounts Group and under this General ledger.
Some of Setting are co. code level and some of COA level.
Cause according to principle One co. code required at least one COA but one COA can control multiple Co. codes.
hence based on setting of Org. Structure the level and setting, configuration and activities are works.
I feel this will help you.
Regards
Milind Joshi