Dextrose - a simple sugar, usually made from maize / corn (usually) which is chemically identical to glucose. This differs from table sugar, sucrose, in that sucrose is 1:1 ratio of glucose and fructose that are chemically bonded together: Fructose is a simple sugar mainly found in plants such as fruit. Fascinating, huh? Na, it isn't. However, yeast has to do a bit more work with table sugar. To quote the marketing stuff;
'Brewing sugar is Dextrose Monohydrate. The main difference in the use is that it is a Mono Saccharide (one molecule of glucose) as opposed to household sugar which is a Di-saccahide (2 molecules). This means that fermentation using brewing sugar will start quicker and ferment cleaner. Normal household sugar has to be 'split' by the yeast which produces bi-products and impurities. These bi-products can have a taste which may slightly affect the taste of home brewed drinks. We recommend using brewing sugar for optimum results.'
Now sit back and await a heated debate as to if this is really applicable on the homebrew scale. I shall offer no opinion.
Spray Malt is spray dried malt extract, i.e. malted barley is mashed, as it would be if you were all grain brewing from scratch, ten the resultant liquid is boiled / spray dried into a power that you can re-hydrate at home to give you lovely barley based wort. Its basically a dried version of liquid malt extract, a hopped version of which is what you get in the brewing kit cans. Some people think that spray malt, or dried malt extract (DME) gives better results than using liquid malt extract. Again, I shall offer no opinion.
Malt extract can come in a number of 'colours' - extra pale / light. pale / light, medium, dark, extra dark. The more colourful ones have had other grains added at the mashing stage to give their different colours and flavours, exactly like you would in your mash tun at home if you were all grain brewing. Some people use the different types for convenience, some people start with pale and steep speciality grains as part of their brewing process to get the type of resultant wort they want.
Hope that helps.