SELECT 
	u1.Name AS first, 
	u2.Name AS second
FROM Tickets t 
INNER JOIN UsersTbl u1 
	ON t.Reported_by = u1.Id 
INNER JOIN UsersTbl u2 
	ON t.Assign_to = u2.Id

SELECT t.*, u1.*, u2.*
FROM Tickets t 
LEFT JOIN UsersTbl u1 
	ON t.Reported_by = u1.Id 
LEFT JOIN UsersTbl u2 
	ON t.Assign_to = u2.Id

SELECT	UsersTbl.Name AS first, UsersTbl.Name AS second
FROM	Tickets
INNER JOIN	UsersTbl ON Tickets.Reported_by = UsersTbl.Id -- Fine, upto this point
INNER JOIN	UsersTbl AS UsersTbl_1 ON Tickets.Assign_to = UsersTbl.Id -- Here, you are accessing the table with alias name "UsersTbl_1"

/*Hence, the above query is equivalent to the below query*/
SELECT	UsersTbl.Name AS first, UsersTbl.Name AS second
FROM	Tickets
INNER JOIN	UsersTbl ON Tickets.Reported_by = UsersTbl.Id AND Tickets.Assign_to = UsersTbl.Id -- You can move the condition up like this
INNER JOIN	UsersTbl AS UsersTbl_1 ON 1 = 1

/*The above query is again equivalent to below query*/
SELECT	UsersTbl.Name AS first, UsersTbl.Name AS second
FROM	Tickets
INNER JOIN	UsersTbl ON Tickets.Reported_by = UsersTbl.Id AND Tickets.Assign_to = UsersTbl.Id
CROSS JOIN	UsersTbl AS UsersTbl_1