Yes, we can know about the angels -- because God has told us about them in His Word, the Bible. It tells us that angels haven't always existed but were created by God before He made the universe. When the world was created, the Bible says, "all the angels shouted for joy" (Job 38:7).
Why did God create the angels? They were meant to be His servants, obeying Him and doing His will in the world. Because they are spiritual beings we're seldom aware of them -- although on occasion they do become visible. They protect God's people and watch over them -- not just to preserve them from physical harm but to shield them from Satan's power. After Satan failed to persuade Jesus to sin, we read that "angels came and attended him" (Matthew 4:11).
Although I know it's a popular idea, the Bible says we don't actually become angels when we die and enter heaven. The angels are different from us, and even in heaven that difference is preserved. But that shouldn't discourage you -- because heaven will be far more glorious than anything we can imagine right now. In heaven, the Bible says, Christ "will transform our lowly bodies so that they will be like his glorious body" (Philippians 3:21). Think of it: Some day you will be like the risen Christ!
Thank God for His angels, and thank Him also for His love for you. Thank Him most of all for the salvation He has provided for us through His Son, Jesus Christ. Have you invited Him to come into your life, and are you trusting Him alone for your salvation?