Just open an account on Moneypot and make a deposit in your account: then you will find the "invest" option that allows you to do so istantly and without any fee.

Return is not fixed nor knowable someway in advance: investing in moneypot basically means you provide your money to house bankroll; so when players, of all different apps implemented in MP, lose  you win and viceversa.

If I got it right, ipotetically you may assume in the long run you will see your investiments growing by a percentage equal to average houses edge, of all MP apps,  weighted by the respective wagering volumes.  But lady variance will likely disagree with this