I'm a bit confused - you mention special compost, which might imply you're potting it up, or it might mean you still want to plant it in the ground. If you're potting it up, use John Innes No 2 or 3, if in the ground, dig over where you want to plant and add any well rotted compost to improve the soil a bit.

As for actually planting, it depends - if the tree is bare root and in a plastic bag, it will need some protection from the cold weather till its hardened off, but you need to get it planted within a few days. If its already potted and was outside at a garden centre, then you can just plant it straight out as soon as you've prepared the planting area.