Type : sam_iEnableCheats=1' and hit enter : without quotes

press ESC and F1 to open the cheats window :

hud_bShowPing = 1
hud_iShowBandwidth = 1
hud_bShowCrosshair = 1
sam_ctMaxDebris = 20
sam_bEnableRagdollDeaths = 0
prf_bShowFPS = 1