I had a similar experience when I was younger. People told me I "just have to have faith", but it was hard to understand what they even meant by that. How can you have faith in something you don't even understand? It was only later that I realized that faith is not necessarily "blind faith". Blind faith is believing in something without any evidence. But you can have faith in something precisely because you have discovered good reasons to believe it. Some people can believe without question, no problem. But others, like myself, need some good reasons first. Luckily, there is a long history of Christian apologetics (referring to "giving an explanation or reason", not "apologizing" for something), and if you're serious about wanting answers to your questions, you have only to look. A very good starting point is the book Mere Christianity by C.S. Lewis. You can listen to the audiobook for free on YouTube.

To address your questions about those who died before Christ came, or who never heard of Christianity: First of all, if God is all-knowing, then He knows exactly what is in a person's heart. He wrote His law, or moral code, onto our hearts (you might refer to it as your conscience). We are all aware of the essence of what He wishes from us (don't steal, don't murder, don't cheat, etc), whether we've heard of Christianity or not. But the more we are aware of, the more responsible we are for our choices. If a person has heard of Christianity and chooses not to follow Christ, he is held responsible for that decision. But if a person has never heard of Christ, his ignorance is no fault of his own. God knows the state of his heart, and he will be judged fairly in proportion to what he can be held responsible for, such as acting in accordance with conscience, God's law that is written on his heart.

God sees all time, past, present, and future, simultaneously. He knows the states of all souls before Christ came, as well as after. And if God is the measure of all goodness and all justice, then we can be assured that we will be judged fairly and with mercy.