Can anyone help with some Sibelius questions?

I'm trying to input a tuplet through step time.  I would like the rhythm to be:

1 8th note and a 3 note 16th note triplet.  When I try to do this right now I put in an 8th note and then tap ctrl 3 to set the tuplet, click the 16th note and when I look up I see an 8th note triplet begun.

Can anyone help me please?

Keith is dead on!

If I'm understanding you correctly, you need to input your 8th note, then input your 16th note on the ";and";, then with the 16th note still highlighted, hit ctrl+3 to start the triplet.

A triplet will start with whatever note is highlighted.

Hope that helps.