So I'm buddhist, so I feel obliged to comment. I belong to the American Zen sect of buddhism. The main thing to keep in mind with Buddhism is that its incredibly unorganized. For example, East and Southeast Asia are all mostly Mahayana Buddhists, but each nation has its own dominant Mahayana sect, and even if the dominant sect is the same in two countries they'd still have different customs and beliefs depending on the areas. It goes all the way down to the local community level
The main things we believe though are fairly simple. All life is full of 'suffering' (we call it dukkha) which is defined very very broadly. The root cause of suffering is desire, which again, is defined broadly. we dont just think of suffering as like, being sick, or poor, or hungry, though those are all valid examples. Nor is desire simply wanting an object. Suffering is a essentially a state of not being at peace, a state of...well, non-equilibrium. Desire comes in different forms, but the way I see it its essentially trying to force things through your will out of a natural state. The goal then is to end desire, which should end your suffering. To do that, the Buddha created this thing called the Eight-Fold Path which serves as tenants to follow to help you reach the state of the cecession of desire. These tenants are virtually the same as most religions around the world, including Christianity
Keep in mind, I'm just a novice in my sect, and some of what i say may be lost in translation, or other sects may word or think of things differently. The main point is that there's no one right way to enlightenment, and different sects may take different approaches but still get there.
Also, in respect to an above comment, I believe in reincarnation, but its virtually independent of karma. The buddhist view of reincarnation is different from the traditional (hindu) view of it, but thats a long discussion for another time. Even then, I don't think i subscribe to the majority view when it comes to buddhist reincarnation, but the main point to keep in mind is that it doesn't involve a soul per say, as we dont believe in the existence of a soul, at least one in the western conception. In addition, in response to the OP, we dont believe in a supreme absolute law in the way im assuming your thinking of, nor do we believe in sin. I personally dont believe in an absolute good or evil, but i still consider myself to be a person of very strong morals. I'd really rather do literally anything then get in an argument about ethics though.
But yeah, hopes this helps you understand Buddhists at least a bit more. Honestly, and this is just my opinion, but I know that when christians try to actively convert me, it immediately turns me off to the concept. If you want to talk to them about religion, keep it respectful. Don't just go in with the attitude of "I'm right, your wrong and i want to make you see my way." Just understand they believe what they believe for a reason, often a very personal one, so basically just dont be a jerk about it is what im saying (not that I am calling you a jerk, i dont even know you)