Hello and welcome, mamalynn
First of all, yes, absolutely it's ok to just read other posts -- you can glean a wealth of info that way. There's no pressure to participate -- any level of involvement that is comfortable for you is just fine!
In terms of "getting in", are you asking about how to to post/reply? Try clicking the title of the thread you want to reply to, and in the upper right corner there should be a small green "reply" button. Hit that and a text box will open up where you can type. When you're done, scroll down a tad and there will be 2 buttons below the text box, one says Post and another Preview. Make sure you have Internet before clicking one, then you are set! Let us know if this doesn't quite answer your question.
Glad you found the group -- people here really get it about having a family member with BPD. No matter how weird, intense, traumatic, bizarre, whatever, this is a place for you to read, share, learn, and be yourself.