What did Paul mean when he said Christ sent him not to baptize?

Paul meant his primary apostolic commission was not baptism, as John the Baptist's was, but preaching the gospel. That gospel is that Christ died, was buried, and rose again, proclaimed without human wisdom so the cross of Christ would not be made of no effect.

Les explains that 1 Corinthians 1:17 shocks many people, but the Holy Spirit moved Paul to write that Christ did not send him to baptize as He sent John the Baptist. John's ministry was to baptize with a baptism of repentance. Paul's mission, by contrast, was to preach the Gospel—that Christ died, was buried, and rose again—not with wisdom of words, lest the cross of Christ be made of no effect. The preaching of the cross is foolishness to those who perish, yet it has everything to do with us because there God has His controversy with man.

1 Corinthians 1:17

For Christ sent me not to baptize, but to preach the gospel: not with wisdom of words, lest the cross of Christ should be made of none effect.

Was Paul sent by Christ to baptize, and if not what was he sent to do?

No. Paul declares Christ sent him not to baptize, unlike John the Baptist whose ministry was baptism of repentance. Instead, Paul was sent to preach the Gospel—that Christ died, was buried, and rose again—not with wisdom of words, lest the cross of Christ should be made of no effect.