after " by " what is correct to use after "by" in sentence ??? infinitive or verb+ing ???

New Year Happy New year 2016 for all :)

Miss ... Hello my italki's friends I missed you all , it was busy week I did many important things now I'm here again for meeting and discuss a lot . I'm waiting you :)

I've received , I received ... Explain the grammar ! Who can advise me with basic grammar rule according to : 1- I've received 2- I received when can I use each one in the sentences ?

Can , Could I know could is the past of can ... but many time could use in simple terms any grammar to use Can and Could !!!

is there any Group Skype conversation ?

Best way to practice English ! I'm new member here , and I'm interesting to practice English with people to improve my skills . Kindly advise me the best way !