What it does
This amending Act, cited in the statute as the Electricity Supply Industry Amendment Act 2003 (s 1), operates primarily as an amendment-and-consolidation instrument for a small set of existing statutes that regulate electricity supply in Tasmania and federal competition law references. Mechanically, the Act does three things as recorded in the text you supplied.
First, it sets its own commencement. Parts 1, 2 and 5 begin to operate "on the day on which this Act receives the Royal Assent" (s 2(1)). Parts 3 and 4 are not automatically in force: they are brought into force by proclamation, by time(s) proclaimed, by occurrence(s) proclaimed, or otherwise proclaimed (s 2(2)(a)-(d)). The Act therefore creates an immediate effect for certain provisions and reserves executive discretion for others.
Second, the Act serves as a vehicle for incorporating amendments into authorised versions of existing Acts. Multiple sections across Parts 2, 3 and 5 repeatedly state in identical terms that "The amendments effected by this Part have been incorporated into authorised versions" of particular Acts. Across Part 2 (numerous numbered subitems and repeating text) those target statutes are the Electricity Supply Industry Act 1995 and the Trade Practices Act 1974. Part 5 makes the same incorporation statement in relation to the Electricity - National Scheme (Tasmania) Act 1999 (see, for example, Parts 2 and 5 summaries and sections 3-22 and 42-46 which each state that amendments have been incorporated into the authorised versions of those Acts). The text supplied does not set out substantive replacement clauses or detailed amendment text inside this instrument; instead it records that the amendments have been embodied in the authorised versions of the other Acts.
Third, the Act expressly repeals one specific provision of the principal Act (the Electricity Supply Industry Act 1995): section 39A of that Principal Act is repealed (see the marked s 39 "Section 39A repealed" which states "Section 39A of the Principal Act is repealed"). The repeal is referenced multiple times (including within Part 4, which also includes an editorial comment that some provisions "Commences: Never commenced"). The Act does not reproduce or restate the text of s 39A within the amending Act; it is recorded only as a repeal directive.