Foxgloves (Digitalis purpurea) are normally sown by taking seed from the plants growing in your garden. Wait until late July when the seed is black and rattle in the seed pod.
You can then simply scatter the around your garden and young plants will develop by the autumn. Your may need to reduce the number of plants you get to avoid over crowding. Be careful that some of the plants do not crowd out the other plants you grow as they can be very demanding in plant food terms.
Rather than just spreading the seed around your garden you can sow them in lines in say the vegetable garden. Sow about 1 cm deep (quarter of an inch deep) and lightly cover with soil.
The resulting plants can then be planted out in to their flowering positions in the autumn.
Digitalis purpurea ‘Alba’ seed may not germinate as white white flowering plants and revert to purple. If you need white flowering types purchase and sow seeds now. scattering through out the garden or in rows.