On the face of it, this is a straightforward screen that enables you to establish a player's worth to the squad and in the transfer market as well as manage their availability. Given the conflicting personalities that make up the Football Manager universe, such decisions have far-reaching implications.
The overview outlines a player's worth according to market factors such as his age, recent performances, happiness and stats as well as his current salary and contract expiry date. This will help you to assess your own valuation of the player, which may be inflated if other parties are interested in him, or deflated if you wish to offload him quickly.
The four remaining sections of the screen (Transfer Instructions, Squad Status, Transfer Status and Loan Status) are all useful tools in your management of the player's availability and can also be used to help your stewardship of the club in other areas.

Transfer Instructions
This is where you set the value of your player and can also save yourself a great deal of time to devote to other areas of your club management. By setting instructions for your assistant manager to accept or reject certain offers for your player you can minimise the time you spend on negotiating his departure. This is particularly useful if you are selling a player at a premium to take advantage of his inflated value after a good season or in the event that he is being pursued by several teams. As you will see in the News section, players frequently change clubs for figures that vastly exceed their supposed value. Using these options you'll ensure that timewasters who aren't prepared to do likewise will be immediately rebuffed when they approach some of your top talents.
Note that you don't have to make a player explicitly available by changing his transfer status to set a price for him. This means that you can use a huge price tag to warn off potential suitors, or set a figure that will represent the premium price it would take to persuade you to let a key playing asset leave the club.

Squad Status
One of the key factors affecting a player's happiness is the status you afford him in the squad. When you sign a player you'll assign him a squad status that will reflect your view on how central a role he'll play in your plans. Similarly, current squad players are keen to know where they stand with you.
If you suggest a player is a key squad member he may firstly expect a pay rise to reflect his status and secondly he will demand that he is a regular first-team player. In other words, false promises that a player is central to your plans may easily result in the player becoming disaffected and unhappy.

Transfer Status
Defaulting to No Status Set, this option enables you to send a clear message to your player and rival clubs on the availability of the individual. Transfer Listing the player will immediately alert other clubs and will be taken as an unequivocal sign that you want the player to leave. Most players' happiness will be immediately effected by such a decision and they will either try to fight for their place or be resigned to their fate according to their personality. If you fail to offload a transfer listed player there's every chance they'll become increasingly annoyed and potentially disruptive as a result.

Loan Status
The loan option is very useful on a number of levels. Aside from the bonus of giving young players valuable first-team experience, it can also help you to bring down your wage bill, at least temporarily. In some cases, you can even broker a loan deal that will bring in a lump sum of cash up front.
Many clubs who cannot afford the asking price for a player who is transfer listed will often pursue a loan deal for him - set the loan status to unavailable to deter suitors who may take up a great deal of your time by frequently making such approaches.