Post meta

Get the meta for all keys for the current post

$meta_keys = get_post_meta( get_the_ID() );

Get the meta for single key for the current post

$meta_key_value = get_post_meta( get_the_ID(), 'meta_key' );

Add post meta for given post

add_post_meta( get_the_ID(), 'meta_key', 'meta_value' );

Update post meta field, for given post

update_post_meta( get_the_ID(), 'meta_key', 'meta_value' );