In lesson 1.1 two statements vary in their use of "tu". I assume I'm going to learn more about this as I go, but I want to know now! ;)  The grammatical comment suggests they are the same form. Is it merely for emphasis in the first?
Thanks!
   

Hola Paul,

Tú is a subject pronoun, you  informal, the familiar usage as opposed to usted, (sing/ formal.) Tu is a possessive adjective, your, informal, su your (formal). Hope this helps.
Saludos,
Ricardo

Aha, yes, that explains these two examples. Guess it would be helpful to have more information than "sing/informal" but I'm sure that's coming. Thanks ricardo-rich!

Paul: in fairness, the English translation highlights the difference:
¿Cómo estás tú?....How are YOU?
Gracias por tu participación...Thank you for YOUR participation. 

When I began learning I had a similar difficulty with está, esta, y ésta. At first I thought it was a typo, then realized the presence, absence, and/or location of the tilde connoted completely separate words. It was then that I realized how important that little mark is in Spanish.

Gracias, Dan-H24. Since posting this, I too have learned the significance of the accent!