How do you do a custom format

Hello Andrew, Thank you for the post, welcome to the forum, in answer to your question, in order to undertake a custom format we need to decide what it is that we are going to apply formatting to, for example lets say that our company requires us to have;
All monetary values entered in a particular column range to be as follows;
1. Positive in Blue with a £ sign comma separated thousands and with two decimal places.
2. Negative in parenthesis Red no minus sign and as above for currency.
3. Our zero (0) value is to be the word "Zero" and it should be Magenta in colour.
4. Any text entries must be clearly marked as being "Invalid Entry" and shown in Black.
Thats our requirements; lets set the custom formatting; Select the range of cells to be formatted; lets say A1:A20.
Go to the Menu command Format>Cells and choose the tab Numbers, in the dialog box for Numbers, at the bottom of the list, you will see the option Custom, select this and in the scrollable area scroll downward until you see a format code that is near to or similar to your requirements, in our case just above the 0% option is a Type that we can use as a starting point;
Click on this option, it will appear in the Text box Type, now is the time to set the Custom format as required above.
Click at the end of the line of digits, press the Home key on your keyboard to move to the beginning of the line, observe the entry, Red is enclosed in [] square brackets, type [Blue] and using the direction keys move to the minus sign and delete it, type ( and move to the end of the entry type ) then type semi-colon (;) this is the separator symbol, at the moment we have set for Positive and Negative values, the ; takes us into the area of custom formatting for 0 values type "ZERO", ensure you include the quotation marks (") then type ; moving now into the Text formatting area, type the words "Invalid Entry" again remember to insert the quotation marks, (") in front and behind the text. Press OK.
Now in your worksheet in the range A1:A20 type any value and/or text entry and observe the custom formatting that has been applied.
I hope that has answered your question, if so please click the Resolved link, best regards Pete.