Level 1 characters begin the game with 0 Assets. For the first five levels of play, characters should typically gain 1 Asset per level. For the final five levels of play, characters should gain 2 Assets per level, for a maximum of 15 Assets at the end of the game. These may be gained over the course of the level or at the same time that a new level is earned.
Property is bought and sold at the standard Asset value. So, a character can spend Assets on Property, decide later they don't want it, and sell it for the same amount they bought it for.
For more information, see Player's Guide Chapter 8: Assets and Property.