1. After a normal G/A with flaps 15, does the fd command RWY HDG?
Nope, it commands the track flown as you engage the TOGA mode.
The F/Ds command 15 degrees nose up pitch and roll to hold the
approach ground track at time of go–around engagement.
2. After a engine failure after v1, does the fd command hdg sel, can i change the heading below 400ft agl?for runway track corrections?
Without any prior selection it commands wings level and doesn't care about track or heading. Depends on your SOP of course, in ours it reads: above 400 ft AGL the PF commands HDG SEL or LNAV. In case of HDG SEL you have to adjust for W/C of course.
3.how do you use autobrake on landing? some rules of thumb?
Well, it we're supposed to use minimum autobrake, however autobrake 1 is a normal selection and requires detent 1 reverse, autobrake 2 is normal for wet runways and requires detent 2 reverse, both cases where runway length is not limiting. If runway is a bit short we're free to take whatever autobrake we deem necessary up to max, but of course once we select a setting of 2 or higher we have to use at least second detent reverse to reduce brake wear and lower the brake temperature.
4.for what is the double egine flame out procedure the items both start levers cutoff? is it a reset of the MEC?
To answer that i would advise to read up on b737.org.uk, i took a paragraph from there to answer that specific question.
Note that Boeing policy regarding loss of thrust from both engines is that the only likely causes are fuel mismanagement, volcanic ash, or rain/hail ingestion. In these cases it is probable that an engine can be rapidly restarted if these procedures are performed expeditiously. Therefore, the object of the LOSS OF THRUST ON BOTH ENGINES procedure is to rapidly restart one or both engines and re-establish an electrical and cabin pressurization source. The flight crew should not wait until they are inside the In-flight Start Envelope. Accomplishing the procedure immediately allows the crew to take advantage of the existing RPM on the engines.