Dear HoneyCoders!
First of all, hello- my first post in the community 
Second, the question:
is it possible to create form that doesn't represent one row in table but multiple rows instead?
To be very precise let's use existing template: Timesheet application. When you create new timesheet, in available template application, you need to choose a day (Mon to Sun) from drop-down list and put values in fields "Start Time" & "End Time".
What I need to achieve, is when I get into timesheet I would like to see a table with one column filled (e.g. day from Mon to Sun) and one/two columns where user can put input.
For timesheet application it may not be that big issue to create new line with each day (however it isn't very efficient because it is logical that 99% of situation employee will put hours from Mon to Fri). For my app it will not fly because each time someone will interact with app it will need to create over 100 positions. It will be nightmare to choose position from huge drop down list and each time check if specific position has been added before or not. I'm aware that I can denormalize my table and create all those positions as columns in table but it doesn't seem right (each time I need to change list of my positions I would need to add/delete column).
Hi @Andr-576d, welcome to the community! 
It's great to hear that you're exploring our templates, and how you're looking to customize them. 
To answer your question, yes, you can create a form that submits multiple rows to a particular table or to different tables. You can achieve this through Builder automations, and would use the action "Add a row" to specify which data would be written to which table.
You can add multiple actions to the same automation, and each one could specify writing a different row to a table:
In regards to modifying the timesheet app or applying similar concepts from it, you could create a screen that has fields specified for Monday through Friday entries as you are describing. This could help you control how many entries are for each day.
If I'm picturing what you're asking for correctly, you could just copy the time entry block for each day and pre-select the day of the week. (Let's say allow two entries per day for this example):
To pre-select a day, I used FINDROW() to call a particular day from that table, and I made the data cell uneditable:
Then create a Submit button with an automation with separate actions, that each write a time entry to its own row:
Hope this example helps or inspires different ways of how you could customize this for your needs.
Let us know if you have any questions on this.