I agree with Steve Christian however in view of Ian's comment first remove bark.
Personally I'd rather not use twigs from ground because how long have they been there and do you know what the wood is
Could have started to rot and certain trees quickly deteriorate, Birch in particular.
Much better to cut a few from a standing tree/bush, hardly likely to cause any harm unless you're collected armfuls for resale.
When done in the winter they don't take too long to dry out.
Having been involved, over a number of years in building bridges and Elephant proof fences, in Pound Wood
using Sweet Chestnut which is an excellent building material the first operation is to remove the bark.
Leaving it on the wood only creates a hideaway for various insects including those that make a meal of the material.