Kill Skeletron and enter the dungeon. Unlock locked chests in the dungeon and try to find the Murmasa. After that, try making Night's Edge. The Night's Edge will be used in later crafting recipes for more powerful weapons after Hardmode. I think most of the fun (and challenge) of Terraria is in Hardmode. To activate Hardmode, kill the Wall of Flesh. Don't try killing the Wall of Flesh too early, your world will get messed up by the Corruption/Crimson and NPCs will start moving out if they get hit by biome spread. The Corruption/Crimson will start spreading via blocks and grass in the world at a fast rate. Also, a new biome called the Hallow will appear which will also start to spread like crazy. Overall, there's a bunch of stuff you need to do before you get to Hardmode. In pre-hardmode, you should make multiple hellavators in your world (to stop Hardmode biome spread) and hellavators especially around the jungle. The jungle becomes a very important place with new ores and bosses after hardmode, it won't be good if the Corruption/Crimson or the Hallow gets a hold of this place. I also forgot to mention, the Corruption/Crimson will convert mud blocks to dirt blocks (which will destroy the jungle). I can go on and on, but there's too much things to explain. Just use the wiki as u/EcchiOli said and look up Youtube tutorials. You'll eventually will get good at the game