When editing a text file, the Go to Line item in the Go menu will ask you for a line number, and then move the text cursor to that line. You can enter the line number as a decimal number (just enter the number itself) or as a hexadecimal number (as 0xFF or FFh).
When editing a file in hexadecimal mode, the Go to Offset command will ask you for a file offset, counting the number of bytes from the start of the file. You can enter the offset in hexadecimal, decimal, octal or binary notation. You don't need to format the number in any way (e.g. just enter FF for a hexadecimal offset). Just click the radio button with the notation you're using.
Whether going to a line or offset, you can prefix the line or offset number with a plus or minus sign. The sign makes the move relative to the current line or offset. If the cursor is at line 150, and you go to "100", the cursor is moved to line 100. If you enter "-100" it is moved to line 50, while +100 moves it to line 250. You can prefix numbers in any of the four notations with a sign. E.g. entering a hexadecimal offset "-F" moves the cursor fifteen bytes to the left.