i had no idea how to form a portfolio but first things first started out by ordering a decent folio case. the size of this case depends on what size you would be comfortable with but i would recommend anything of size A3 and above. pick a size best for you as it may feel daunting to tackle a size A1 folio.
presentation is all to do with your style of work and what pleases your eye. but a tip i could give is dont make it too cluttered as this may distract from the things you put into your portfolio give each item the space it needs.
and as for the contents this will depend on what you are applying for alhtough showing a range of skills is good. and if you apply to different schools they may want different things from your portfolio. this also depends upon the course you have applied for.
such as i have recived a letter for an interview next week which has specified that i should not take any garments to the interview. so instead of this i have decided to take pictures of them instead. also be prepared that they may give you a theme to work you portfolio around and may ask you to produce something from that theme.
i would take pictures of mine but i need to charge my camera battery i may post some later when i get around to it.
hope all that waffling on has helped you