trigger Creating_AccountandContact on Lead (before insert) {
    // Names stores company names(Account names)
    list<string> Names=new list<string>();
    for(Lead leadVar:Trigger.new)
    {
        Names.add(leadVar.Company);   
    }
    // Querying list of existing Accounts
    list<Account> listOfExistingAccounts=[select id,name from Account where name in:Names];
    // This map will store company name as key, account as value
    Map<string,Account> accountMap=new Map<string,Account>();
    for(Account accountVar:listOfExistingAccounts)
    {
        accountMap.put(accountVar.Name, accountVar);
    }
    if(listOfExistingAccounts.size()!=null)
    {
        list<Contact> listOfContacts=new list<Contact>();
        for(Lead leadVar:trigger.new)
        {
            Account accountObj=accountMap.get(leadVar.Company);
            Contact contactObj=new Contact();
            contactObj.AccountId=accountObj.Id;
            contactObj.LastName=leadVar.LastName;
            contactObj.FirstName=leadVar.FirstName;
            contactObj.Email=leadVar.Email;
            contactObj.Phone=leadVar.Phone;
            listOfContacts.add(contactObj);
        }
        insert listOfContacts;
    }
    else
    {
        // write your logic to insert new account and contact
    }
}