When Catholics offer our sacrifices, the more correct terminology is we offer them to make reparation or restitution for our sins and the sins of others. Sometimes we may say we offer our sacrifices to help to save somebody, which is often shortened to for the salvation of souls.
Salvation is both a gift from God and our own response. We cannot justify ourselves by any work. Being made right with God is a pure gift that Jesus offers. However, once accepted, we must work hard to respond to His grace, which calls us to follow Jesus and to live out the fullness of God’s call to discipleship and holiness. In essence, it is the work of God, but we must choose to participate, often with great effort.
Part of that discipleship is that we must learn to deny ourselves so to learn to love others more selflessly, promptly and joyfully as Jesus did. To this, it is correct to say I offer my sacrifices for the salvation of my soul.
As for the salvation of others and for the world, Jesus invites us to join our sufferings with His on the cross, to participate in the work of His salvation. While our sacrifices themselves do not change people’s free will, they do increase the graces God has available for the souls who most need them. So in this sense, it is also correct to say I offer my sacrifices for the salvation of souls and for the salvation of the world.