I would like to know how to start a native.TextField with a value already set in it, being this value of type float / decimal.
After you create the field, add this line
mytextfield.text=“mydefaulttext”
thats it 
If you are talking about editing the field, you need to handle it in the listener.
This way it worked, thank you
And as it is done to insert a number of the decimal type, for example 15.52, in the Field Field?
Its the same method. Once you have the number as a string, you can later when you need convert it to a number using
mynumber=tonumber(mytextfield.text)
You will find this all in the documentation from Corona, which is well made,
Best of luck!
After you create the field, add this line
mytextfield.text=“mydefaulttext”
thats it
If you are talking about editing the field, you need to handle it in the listener.
This way it worked, thank you
And as it is done to insert a number of the decimal type, for example 15.52, in the Field Field?
Its the same method. Once you have the number as a string, you can later when you need convert it to a number using
mynumber=tonumber(mytextfield.text)
You will find this all in the documentation from Corona, which is well made,
Best of luck!