Alchemy can be learned as early as Level 1 and unless you have access to herbs through other means, it is strongly recommended you pair it with the gathering profession, Herbalism. Through gathering various herbs along your adventures, you’ll be able to transform them into:
1. Elixirs - typically last for an extended period of time, most commonly increasing a player’s secondary stats. An example of a popular elixir in Classic WoW is Elixir of the Mongoose. When you die, you lose this buff.
2. Potions - usually a quick burst of some type of buff that has an instant or limited uptime. Major Healing Potion and Major Mana Potion are great examples, as well as Limited Invulnerability Potion. Great for both PvE and PvP. You can use potions repeatedly over the course of a fight, as they have short cooldowns.
3. Flasks - powerful buffs that last longer, with their effect persisting through death. Usually require more rare materials like Black Lotus and encouraged use is for raiding. Examples include Flask of the Titans and Flask of Distilled Wisdom. Flasks in Classic WoW can only be created through Alchemy Labs.
4. Transmutes - the ability to transform two materials into a powerful item, with typically a 24 hour cool down. Must be learned through recipes such as Recipe: Transmute Arcanite, which in turn, allows you to Transmute: Arcanite. Arcanite Bar is very powerful, needed for iconic items like Thunderfury, Blessed Blade of the Windseeker and Nightfall.
5. Oils - usually made from fish from Fishing, and a reagent needed for other Alchemy items like Blackmouth Oil.
Alchemy pairs well with Herbalism and Fishing, as reagents from those professions are needed for potions, flasks, and elixirs. At higher levels, Mining ore is needed for transmutes.
Alchemy is a strong profession to have, regardless of your class, if you are interested in endgame content. Alchemy will allow you to craft many consumables that enhance your performance during dungeons and raids.
Here you can buy Classic Alchemy & Herbalism Leveling for EU or US Servers.
Also you'll get guide for completing Classic Alchemy & Herbalism leveling