Glute activation & tight hip flexors

IzzyBooNZ1

Hi there
I have an office job so sit alot during the day. I read that this can cause weak glutes & tight hip flexors. Can anyone recommend an easy to follow YT video or provide info on exercises to help with these? Do i do them before a warm up?

When i do squats i squeeze my bum cheeks at the top, is this correct? I do find it hard to squeeze them. Plus i find it hard to squeeze bum cheeks and keep belly button pulled in at the same time.
Also how do i really know i have weak glutes and tight hip flexors?

Gotta go out but will check this later

Thanks !