If its fresh, meaning not aged or uncomposted, you need to compost it for at least a year before adding to your soil. If its got straw in it, stack it up somewhere and leave it to age prior to use. Note also, if you grow root crops like carrots, manures shouldn't be used because they can cause forking.

As Bamboo suggests, you need to compost it first and not use it where you intend to grow carrots and parsnips. I would not spread it but dig it in. The best time would be in the spring especially if your soil is light for the nutrients will be soon washed away by the winter rains.