Baptism, testimonies etc

Hey all. Thought I'd make an account here to ask something I've been thinking about for a while..
I've been brought up in a Christian household since birth along with my brother and sister, I was baptised as a baby (and later confirmed when I was 11 years old or so?) in what I believe is a Methodist church. Over the past few years I've let other commitments (college etc) get in the way of me going to church, I didn't always enjoy attending "traditional" services and preferred the more engaging and upbeat kinda nature of baptist churches, and in the past few months I've been joining a group of youths with their 12-20 year old group for social events, occasional bible studies etc (I'm 18, soon 19 now)

When with this group a couple days ago, a few mentioned the time when they "became a Christian", which got me wondering what actually defines this point for someone? Surely with similar upbringings to myself they might've felt it since they were involved in church from when they were younger? There was also discussion of what I think was called their "testimonies" that sometimes people share with each other before praying together - could someone explain how that kinda works? Not having that baptist background I'm in the dark really..

Lastly, if I wanted to be baptised in a Baptist church and commit to attending church on a Sunday etc, is this a lengthy process? Or something I can commit to before moving away from this area of the country for my studies?

Hope this made some sense and I'd really value your inputs :)