Buy RS3 Steel longsword
The steel longsword is a tier 20 melee weapon in RuneScape 3. It goes in the main-hand slot and uses the slash style. You need level 20 Attack to wield it. It has 245 ability damage and 316 accuracy, which makes it a solid upgrade for early combat training.
This razor sharp sword can be made at a forge and anvil with 2 steel bars. Smithing it grants 150 experience in total. If you want more power, you can upgrade it to a steel longsword + 1 with 2 more bars.
The steel longsword also drops from Hill giants, Hobgoblins, and Cyclops in the God Wars Dungeon. You can get one by having a rusty sword identified by Tindel Marchant or repaired in a Player-Owned House. It is sold in the Varrock Sword Shop, the Warriors' Guild Armoury, and the Weapon Shop on Anachronia.
Players who like Invention can disassemble it for Base parts, Blade parts, Metallic parts, Sharp components, and Dextrous components. At only 0.01 kg, it adds almost no weight to your inventory. It is a simple, useful blade for any low-level melee build.