Forms :: Inserting ID / SYSDATE And USER Automatically?

I have created a datablock and set up the user interface to allow the users to insert all the data they need, however my table has some fields which should be generated automatically and are not done through user input:

id - which is uniqe to each entry to the table so is gernerate by a sequence (which I created on the database) but when i put seq.nextval into the initial value on the datablock it says i cannot do this, so how do I use the sequence to insert the value into that field in the database. This is my primary key in my database whichobviosuly my users cant input data to, instead it is generated automatically.

User - similarly in the datablock is a user field which states the user that inserted that record, I know on the database i can put DEFAULT user for that field , but how do I make the user insert automatically through forms.

Date - Similarly again how do I set SYSDATE to be automatically input to the date field when the user submits the record?