If you brought plants indoors over winter, or wrapped them up against the cold, then they can now slowly be hardened off. To do this the plant will need to be moved outside or uncovered, during the day and then moved back or wrapped up again at night. Depending on night time temperatures this slow process can take between two to three weeks. If the sun becomes very hot during the day it may be preferable to give it some dappled shade to prevent scorching of the new spring growth. Of course you can just expose the plant to the spring weather and hope for the best, it probably will survive provided it doesn't get frosted, but will suffer a severe check in growth.
Hardening off is particularly important when bringing plants home from a nursery at this time of year. They have probably been grown in nice warm, draught-free greenhouses and will be too delicate for the cold spring weather we're experiencing at the moment.