Please see the documentation of Selenium2Library at [1].
Here is the help for 'Input Text':
Name:
Input Text
Source:
Selenium2Library <test library>
Arguments:
[ locator | text ]
Types the given `text` into text field identified by `locator`.
See `introduction` for details about locating elements.
The `introduction` explains how to use xpath as locator. For example: Input Text | xpath=//div[2]/div/input | 1/27/2016
Since you are a SeleniumIDE user, I recommend the use of an exporter from selenese to RobotFramework at [2].