Hi i'm planning to create a client directory and wondering how will i start on this. does sharepoint has a venue where for example the term store where everyone can have an access to it? this will be used in different site collection. Thanks!
If I understand correctly you would like to have and repository of customers to be used on different site collections.
The issue here is the site collection boundry. There is no out of the box possibility of using lookup fields across site collections (there are some open source projects that enable this kind of lookup field so that could be one option for you)
Another option for you would be to use managed metadata. This is feature of Sharepoint that allows you to use managed metadata fields and reuse them across different site collections (and even different web apps) but its feature is limited you will be basically able to use only a name of the customer. Managed Metadata works best if you have only one datum you want to include (like State, or City name) and you don't need to include any additional information.