Update Sets - what happens exactly?

Hello SN Comm,

I have read a few things when it comes to update sets. I have been able to create a few as well - here is where I am looking to see if someone can just tell me straight forward what happens when I commit an update set..?

short story:

Within our test instance, we have developed a Homepage and a dashboard specific to an Assignment Group. All aspects point to that team just fine. I created an update set for the dashboard and added the portal pages (tabs) correctly. Then I created an update set for the homepage (being able to unload everything that needed to be).

I then went to our Prod Instance, retrieved the two completed update sets and did their previews.

I have not committed just yet. What I want to see if someone can tell me in as straight forward as possible - what will happen when I commit them? For an example to this, If I were to commit to only the update set that has the dashboard and tabs on it, will those things be the only things brought over to Prod instance within the update set?

Both instances are the exact same versions, and I did a clone from Prod to Test just last week - so besides the update sets, they are exactly the same.

Thanks so much to everyone in advance!

-Rob