I need help on how to create a grid structure over my data set with each box being 100m^2.
That isn't manually doing it so I can calculate the features within each box?
You have two options here. First one will create a new vector layer with a grid and the second one will just display a grid as overlay. What you are looking for is the first option. However, in case someone else is finding this question, the second option might be helpful as well.
Edit: of course 10m xy, not 100m as said below...
Run "Create Grid" tool from processing toolbox:
Rectangle as Grid type,
choose your extent and enter
100 for Horizontal spacing and Vertical spacing.
Choose a projected (metric) CRS suitable for your area of interest.
Click run and a new temporary layer will be created. You can save this if you want.
View --> Decorations --> Grid. Enable it and
set intervals to 100. Choose the style you wish it to have. This requires your project to be in a projected (metric) CRS.