It's easy to get started using Evernote for Salesforce:
Get Evernote Business for your company and create your own Evernote Business account.
If your business doesn't already have a Salesforce.com account, create a Salesforce.com account for your business. Evernote for Salesforce is available at no additional cost for customers using both Evernote Business and Salesforce.com's Group, Professional, Enterprise, Unlimited, Force.com, or Developer editions.
An administrator for your Salesforce account will install the Evernote for Salesforce managed package. See the Evernote for Salesforce Installation and Administration Guide for installation details.
Once you have Evernote for Salesforce installed, you can start using Evernote Business to create notes and link them to your Salesforce records.