Question: Is there a difference between evolution and natural selection? Can a Christian believe in either?
My Response: Christians are not defined by what they believe but by Who they believe in. Faith in the death, burial and resurrection of Christ is the bottom line. A personal relationship with Jesus is the definition of Christianity, not the embracing of a defined list of acceptable positions. After entering into a relationship with Christ, the Holy Spirit is committed to guiding us into all truth. While issues, such as the one in this question, are important, they aren't the issues that define Christian faith. Having said that, I want to respond to the specific subjects in the question. Are these positions biblically supported? Can you be biblically sound and believe in evolution and/or natural selection?
Natural selection is a process that is observable in nature. Negative traits and weaker organisms are removed from the gene pool by natural processes. Changes by natural selection occur within species and involve no change between species. I don't know of any reason a creationist would struggle with this concept.
Microevolution is similar to natural selection in that it involves changes over time within a species. There is likewise nothing here that conflicts with a creationist perspective.
Macroevolution is where the tension and disagreement occurs. Macroevolution involves changes "above the level of species" and changes one species into another species altogether. While defended by evolutionists, this form of evolution is not observable or demonstrable because of the time factor purported for this type of change. Macroevolution is rejected by most forms of creationism.
Can a believer accept macroevolution as the method God used to create the world? Many do. I do not. However, this should never be construed as a salvation issue. Hebrews describes faith as believing that God created the world. That is a non-negotiable for believers. The method or means of creation will most certainly be debated among genuine believers until we get to heaven and know "the rest of the story!"