There are two types of transfers available depending on your existing broker - ACAT which is mostly automated and DTC which is manual. Stake supports both. 

On Stake, ACAT transfers are free.

If your broker is a DTC only broker (not part of the ACAT system), there is a $15USD fee per stock position that Stake has to pay to receive your position. You will need to pay this fee for your stock to transferred to Stake. 

It's worth noting that your existing broker may also charge you an additional fee - so contact them before you move your holdings.