I have a (i.e. only one) helpful flag on my profile page and being relatively new to this community, am not sure what it means. Is it a good or bad thing and why/how did I get this?
If you click on the number, it will take you to a summary of your flagging history.
When you flag a post (for not being an answer, or for rudeness, or for being a duplicate, etc.), it gets extra attention by high-rep users who can take action to close/delete the post. Or in cases of custom write-your-own-text flags, only moderators will see the message, and they can choose to take action based on it.
If the high-rep users end up doing what your flag suggested, it is automatically marked as helpful. If the moderator who sees the flag agrees it was a good thing to flag, they will mark it as helpful (this is independent of whether they actually take action or not). Thus helpful flags are a good thing -- they indicate that the community things you did a good job bringing something to our attention.
By the way, after a while everyone accumulates a few unhelpful flags too. Don't stress over those, but take them as feedback from the community that you don't need to worry about those posts.