Telling my parents about counselling?

I recently went online onto a child-help site for kids and young people, where you can talk to trained, proffesional counselors when you need to.
I spoke to a few of the people there about how depressed and sad I felt, and they told me I need to get some help from a doctor/ therapist.
My parents don’t know about this. I tried speaking to my mum a couple of times but she brushed me off.
I need to tell my parents about seeing someone, but I have no idea how. I’ve checked a couple of websites but they haven’t been very helpful.
Any ideas?