Hello
my routerOS have access to 4 to 8 different internet connections through LAN and each connection has its own bandwidth and i want to use it as a gateway for internet.
how can i manage routerOS to recieve one file from all internet connections and send it to PC which requested it?
if you need any more detaile please ask me. 
Thanks
What you are asking about is bonding. The only way you can bond with a MikroTik the way you are thinking about is to either contact the ISP (assuming all of the connections are from the same one) and ask them if they support any bonding and ask them to set it up for you, or to control/own the other end of the bonded link at a central location with more bandwidth that you can download from. Both of which I’m guessing are not options for you.
The closest you can get is load balancing the lines, but that only lets you get the maximum amount of bandwidth of the line your traffic is currently going through or coming from.
I have read of some appliances that supposedly support this for TCP connections, but they tend to be rather expensive.
imagine you are using a download manager for downloading. it opens 8 connection for example
how to manage mikrotik to open any connection from the interface which has the least connections open!!
how to manage mikrotik to open any connection from the interface which has the least connections open!!
You can’t.
You can use PCC to more or less randomly choose an interface, though.
Rather, the way the interface is chosen is strictly deterministic, but can be based on the source port - which will change with each TCP virtual circuit.
can tou tell me more about PCC?