Guide-level explanation
This command looks as follows:

REFRESH STATS <TARGETS> [FULL | LITE] [CLUSTER] 
REFRESH STATS db1.tab1, tab2, db2.*, *.*, 

• takes a list of targets separated by comma, which can be any of the following formats.
  • tab1: tab1 under current schema.
  • db.tab1: particular tables
  • db.* : all tables under schema db
  • *.*: all tables in this cluster
• [FULL | LITE] names the type of loading initial statistics.
  • If the option is omitted, it takes the value from config lite-init-stats.
  • Explicit FULL refers to lite-init-stats=false
  • Explicit LITE refers to lite-init-stats=true
• If [CLUSTER] is set, initialization of statistics happens for all TiDB instances. Otherwise, initialization happens to the TiDB instance connected only.
  Any users, including BR, with read permissions to the tables, can use this command to initialize the stats for the table.