Welcome to the boards, DoodleBob.
I'm going to answer all of these in the most basic, broad, and simple way possible, just to kind of get right to the heart of all this. Then we can talk in more detail from there as you'd like to!
What people mean when they identify as bisexual is generally some variety of "I can experience sexual attraction to people of more than one gender." So, the "signs" would be experiencing that and wanting to call it bisexuality, in a nutshell. How you figure out who you are attracted to is just by observing your own feelings over time; over a lifetime, really.
If by "experiment" you mean you want to have a sexual interaction with someone outside of an ongoing relationship, or an intended romantic relationships, then that's what you tell them you want so that can be a choice both of you gets to make. That way, too, you aren't likely to be having casual sex with someone who doesn't also want that.
(How you find out the orientation of others is by them telling you, and by doing your best to only ask someone for that information - if they're not volunteering it - when it's really information that's actually relevant to you and are in a position of intimacy with someone for that to be appropriate. This is a bit more complicated than the other stuff here.)
Heterosexism and bi/homophobia still loom super-large in most of our worlds and cultures. So, pretty much everyone has internalized at least some of it.
Are you asking why you deny, to and for yourself, that you're some variety of queer? If so, then a) looks like you have your answer to the "am I queer" flavor of questions
and b) probably because you feel scared because of heterosexism, homophobia (I don't know what you mean by being "scared of the labels," but whatever that is, that's one place you already know for yourself you feel scared), and what they can mean and feel like.
Phew! Again, those answers really are me making it as basic as it gets, so they are all going to be over-generalizations, as this stuff is so, so personal. So, where do you want to take this from here? Anything in any of that you want to dig into to talk about more specifically?