confused making function.. please help me

i just tried another day to make function like automation in Airtable. but, it's not easy and i'm about to give up..

for the last time, i would like to ask help.

i'm building private car care reminder service.
  • Table A : carwiki, each car has its own care interval information.
    • car_id : 1 / washing interval every 3days / and so on
  • Table B : mycar, a user add one's own car to get reminder.
    • mycar_id 1 : user_id 1 / car_id 1 / recent washed day... 
  • Table C : reminder, a user gets reminder generated by one's cars interval days
    • reminder_id 1 : user_id 1 / car_id 1 / next car washing day... 

2. Problem im facing
i wanna know how to set up function to generate reminder automatically with function. because i have no idea how to fetch each cars interval using relation in function stack maker. 

i tried like this
  1. input : myplant info (from frontend.)
     : user_id, car_id, recent washed day...
2. calculation ---- this step, i can't load interval days from car_id table. i have no idea how to to day with data relation in function stack..
3. create record --- still.. cannot do that. it's too hard.

please let me know more details steps... 

once i get what i have to do by steps, i even can make a tutorial videos for people like me who are not really used to backend system.

looking for trigger & automation guide

is there any guide about < trigger & automation >?
just like Airtable, i would like to make automated tasks when a record row is generated -> create new row in another table

ex. when a new record is generated in a table, then create another record in a different table based on the values.

what kinda guide do i have to look at? 
i watched function, custom function, background task video.. but all of them are not about trigger based automation. so frustrated.. please help me

adding date to +N days.

i just cannot understand concept of calculation in Xano. 

please help me out to use Xano.

  1. just like Airtable, can i add days from a day with function?
  2. just like Airtable, can make a timestamp record with date record + time record( the value is like ' 00:00 ' )