The forum is opened for everyone who will abide by the rules. Is every board on the forum opened to everyone? No. There are some boards that unless you are a mod/staff you can have access to it. Well, in reality, those boards are just for administrative stuff so, nothing to worry much about.

Yes, again you can. But I strongly advised beginners to read more first, than to be in a hurry to make a post. Because it is always likely that whatever question they may have to ask has already been answered. The only exception is when there is a more recent information or unique angle to it.