To create a new transaction click the New Transaction button at the top right of the account register screen.

You can also create a new transaction by typing ⌘N.

The New Transaction box is located within your account register. This is where you input the transaction details.

If your account register is sorted by Date Descending, the New Transaction fields will appear at the bottom of your account register. If your account is sorted by Date Ascending, the fields will appear at the top of the register (just below the column headings).

Press the "Enter" key when you've input the new transaction details. 
If "Beep When Transactions Change" is enabled in your preferences, you'll hear the cash register sound to confirm the transaction has been entered into the register.

Editing Transactions -

Double-click on an existing transaction to edit it. The fields will become editable and you can make the necessary changes.

When you're done, press the "Enter" key to confirm the changes.  

Alternatively, click away from the transaction in the account register, and you'll see a prompt asking you if you want to save the changes to your transaction.

Creating Split Transactions - 

Sometimes you may want to create a transaction containing more than one category.

For example, you may make a purchase at a grocery store with is partially groceries and partially a reimbursable business expense.

To split a transaction into several categories, create or edit a transaction, then select the Category field. This will open the Category menu - select the “Split” button at the top (or press ⌘-L or Ctrl+L on your keyboard).

To record a split, click the "New Split" button (or use the keyboard shortcut ⌘-N or Ctrl+N) for each split you want to enter, then specify the amount, category, and memo for the split.

Click the Done button when finished (⌘-W or Ctrl+W).

When entering a transaction, if you enter the full amount into the payment field, before opening the split window, each split entered will calculate the remaining amount.

For example - Enter £100 into the transaction payment field, then select the "Split" button. Amend the first split to £40, and select 'New Split'. This will create the next split with the remaining amount, £60.

Quick Entry -

The quick transaction entry interface is an easy way to enter transactions from within the search box.

Typing an amount and description into the search box at the top right of the account register will bring up a quick entry interface.

Moneydance will “guess” the account and category of the transaction based on how you’ve categorized similar transactions in the past.

Click the “Edit” button to change the transaction and the “Record” button to enter it into the register.

The Quick Entry interface is not available through the Reminders view, Loan registers, the Budget screen, or when using graphs and reports.

Auto Complete -

Moneydance has an auto-completion feature for transactions. Transactions can be auto completed by typing into the payee (description) field.

With each keystroke, past transactions are searched for payees with names that begin with the text already entered.

If a matching transaction is found, the rest of the current payee field is filled in with the matched payee value. At this point you can either continue to type, or use the TAB key to continue to the next field.

Using the down arrow while auto-completion is active will display all address book entries and recent payees that begin with the text already entered, and allow you to select one of them.

You can opt to have auto-complete be case sensitive or non-case sensitive. You can edit this option within your General Preferences.