Spells Known of 1st Level and Higher
At 1st level, you know two 1st-level spells of your choice from the warlock spell list.
The Spells Known column of the Warlock table shows when you learn more warlock spells of your choice of 1st level and higher.
A spell you choose must be of a level no higher than what's shown in the table's Slot Level column for your level. When you reach 6th level, for example, you learn a new warlock spell, which can be 1st, 2nd, or 3rd level.
Additionally, when you gain a level in this class, you can choose one of the warlock spells you know and replace it with another spell from the warlock spell list, which also must be of a level for which you have spell slots.