From Wiki - Milky Way Idle

Skills is one of the nine non-combat skills in Milky Way Idle. The player can gain Experience to level up this skill by {{{action(ing)}}} {{{item1}}}. There are seven tiers of {{{item2}}} that the player can unlock by leveling up Skills. The time it takes to {{{action}}} increases accordingly to the tier of the {{{item3}}}. The player can reduce the time it takes to {{{action}}} by using {{{tool}}}.