Hey @Ana Mesas
To mirror objects it's kind of "easy".
1) Select the subject/ object you want to mirror.
2) Properties Panel scroll down to near the bottom.
3) Choose the mirror option.




Grouping is similar
1) Open the layers panel (Top right corner)
2) Select the layers you want to group Hold Shift + click
3) Press group button


Cheers
O. Nate