I set an animation to be played when the left mouse button is pressed, but when I press the left mouse my character goes into a t-pose.
Setup your animation to play as a montage and use the Play Montage node to play it and it will automatically return to the animBP anims. These should help get you in the right direction:
A new, community-hosted Unreal Engine Wiki - Announcements - Unreal Engine Forums19-_Playing_Our_Animation_Montage_in_UE4
Thank you very much!