You will need to set up the ThingSpeak 'thingtweet' control and link to a Twitter account to get an API key for transfers. I haven't had a lot of time to play with this, but the Twitter account I've set up is ArmyOfThings.
This is the most basic code which worked and there's plenty of scope for experimentation and improvement here.
TOP
cls
Textbox MyData
button "Click to send " [postit]
wait
'
[postit]
OPString = "api.thingspeak.com/apps/thingtweet/1/statuses/update?api_key={my API key}&status=" & MyData
print wget(OPString)
wait
goto TOP