Welcome to the forum and to the hobby Kay.
Betta and guppies are thought to be hard to keep together but it really depends a lot on the individual fish's personality. Some bettas do fine with guppies, I have had several in my life that did. Other bettas seem to not do as well with a guppy. My 2 present bettas live in a 45 gallon with a few dozen endlers and in a large community tank with fish much larger than a betta. In each case the betta has been in that environment for well over a year, the one in the large tank has been in that tank about 2 years.
Since you just set up your tank, you will want to read up on fishless cycling a tank. It can make all the difference in your enjoyment of the hobby if you are not constantly worried about the first fish surviving. There is a link to the fishless cycle thread in my signature area because so many people who are new to the hobby seem to need it.