Most organic reactions fall into a few kinds, named for what happens to the molecule. Knowing the kind tells you the product.
Combustion burns a compound in oxygen. With enough oxygen a hydrocarbon gives carbon dioxide and water: CH₄ + 2O₂ → CO₂ + 2H₂O. With too little you also get carbon monoxide, a poison, and soot. This is how fuels release energy.
Addition adds atoms across a double bond, turning it into a single one. Ethene plus hydrogen, with a nickel or platinum catalyst, gives ethane (hydrogenation, how vegetable oils are hardened). Ethene plus water, with an acid catalyst, gives ethanol. Bromine water turns from orange to colorless when shaken with an alkene, a quick test for double bonds.
Substitution swaps one atom or group for another. Methane and chlorine in ultraviolet light swap H for Cl to make chloromethane and HCl. A hydroxide ion can replace a halogen to turn a haloalkane into an alcohol. Elimination does the reverse of addition: it removes a small molecule (water, HCl) from neighbouring carbons and leaves a double bond, as when hot acid turns ethanol into ethene.
Oxidation adds oxygen or removes hydrogen. A primary alcohol oxidizes to an aldehyde and then a carboxylic acid (wine left open turns to vinegar); a secondary alcohol stops at a ketone. Esterification joins a carboxylic acid and an alcohol, with an acid catalyst, into an ester and water: acetic acid + ethanol ⇌ ethyl acetate + water. It stops short of complete, which a later course explains as equilibrium.