If you have an online web broker, the rights issue document should have been sent to you under the corporate actions notification section. There should also be a section under corporate actions that allows you select your response to the corporate action ie. to not take participate, to participate and you would indicate the number of shares that you are interested in purchasing at the rights price.
If you have a regular broker, you could call them and let them know your intentions in relation to this rights offer.
STB Price at posting:
$1.01 Sentiment: None Disclosure: Held