Since I don't recall seeing clear, concise answers -- and, to be fair, all this is discussed in countless existing GV threads, don't overlook the search function or site-restricted Google search:
i have a google voice account (i just realized i have it and dont know how it works), so can i use that for my texting?
You can. Senders need to send SMS to your GV number. Texts to your cell number will count against your text plan. You are stuck using the GV app for messaging (unless you enable SMS forwarding).
can i just send and recieve texts from that number all the time if i get the app for droid and will that take away from my phone's texting plan?
Yes, you can send and receive SMS (no MMS) with the app. No, it does not count against your text plan. GV uses data for text messages.
However if you enable SMS forwarding (it's not enabled by default) then you can receive GV SMS via other messaging apps such as Handcent and ChompSMS. The forwarding feature forwards text messages to your VZW number. If you have this or any SMS voicemail notifications enabled then those messages will count against your texting plan. There are additional caveats with SMS forwarding that you want to be aware of before using.
does the app have to be open?
Nope. Typically you need to open it once after any install/update though.
Also be aware that it's not uncommon for SMS delivery times to have delays with GV. It's intermittent. I find if I manually tell the app to sync that it will receive new messages. In general, I know I have a new message because I also use the GV extension for Chrome (on my work and home computers) and it doesn't have any delays in my experience.
because a lot of these threads don't nail down the details.
A lot of threads do cover the details. I've posted in many of them myself. If you need help searching then ask for it.