If you want to make an offer for a player, go to the Transfers Menu and under the Negotiations tab, you will see the available players. After making an offer you will still be able to adjust it. Don’t forget that there is an entry fee and a 1 Token fee for each Token you offer.

The option is also available directly in the squad of other Managers who are in the same competition with you, and for those players who have 3-5 stars, are close to earning the next star and don't have more than 99% of quality.

Note that the Negotiations feature is unlocked once you reach club level 4 and is only available in the last week of every season.