You can do so many things with the Stories app on Instagram that you don't have to go anywhere else. But if you want to up your game, experiment or just have fun you might like to try some of these apps. Apologies in advance if these aren't available on Android.
Unfold - beautiful layouts for your Stories. You can add images or videos into the blank boxes.
WordSwag - a great app for adding text to your images. Lots of design options and you can choose Stories when you crop your image, so that it's the right size.
CutStory - super handy for cutting a longer video into 15 second clips. If I have more than 15 seconds to say then I shoot my video outside of Stories (making sure I shoot in Vertical mode) and then I upload into CutStory and it cuts it into 15 second parts for me. I can then add text, links etc when I upload it into my Stories.
VidClips - A great tool for putting your little pieces of video together either for a 15 second clip for Stories or longer for IGTV. You can choose the video ratio for square, horizontal or vertical for Stories/IGTV. (just watch out for all the ads!)
If you use an app for iPhone or Android that isn't listed here please let me know about it and I can add it to the list.