If you need to tie a Note to a particular account for a contact, there are two ways to do so.
To illustrate, let's take a look at the Accounts page for a client:
Now, let's say that we want to attach a Note to one of these accounts.
The first method would simply be to create a Note for the client, from whatever area of the database you're currently in. Then, from their Notes page, you would select "Link to an account" from the Note's Actions menu:
You'd then receive a modal where you can select from any of the client's accounts in your database to tie the Note to:
This linkage will then show up directly beneath the Note:
Clicking the Account number within the Note will take you directly to the Details page for the Account, where if you scroll to the "Other" section, you'll see that there is a Note (or multiple Notes if you've linked more than one) and can click the number to see any linked Notes.
The second method to link a Note to an Account is to add it from the Notes section on an Account's Details page. Below we are looking at the bottom of the Account Details page for the Account we linked a Note to above:
You can see that the Account already has five Notes linked to it. If you clicked the number "5", you'd see all Account Notes for this particular account.
First, note that you see the previous Note linked to the Account, plus any others linked to the account (not all five are displayed here). To add another one, click Add Note and you'll see the Add Note modal. Just enter your Note as usual and, after adding it, it will be linked to this Account.
Regardless of which of these methods you use, the linked Note(s) will then be on display within the Account Notes section of the Account Details page for that account, as displayed above.
Also, Notes linked to Accounts will display on the Contact's main Notes page, just like other Notes.