• Well done coming up with a working program and showing your code to the world with the intention to improve! I will tell you some things I would do differently:
• Always indent your code!
• Don't be afraid to leave blank lines in order to group statements
• You are missing the return type of the main function
• Use descriptive variable names (self-documenting code)
• Most people put whitespaces before and after operators
• You do not need to separate strings or \n when streaming
• You can stop loops with the break keyword
• You do not need the if (i == 5) i++;
• Instead of misusing i as a status, you should either use an enum for multiple status or a clearly named variable, so that other coders can understand your intentions easily
• Have your editor auto-remove trailing whitespaces
• For a password check, you can use an early return, if the password was not correct. If the password was correct, the program flow will continue
• Remember that your program is not cryptographically secure. Passwords should never be hard-coded and never be stored in plain-text. However, since you seem to be a beginner, that's not really important right now :)
• I observed Bash not putting a newline after a program exits, so I recommend writing std::endl at the end of execution, so the next commandline input prompt does not get added to the end of your program's last line of output.

#include <iostream>

using namespace std;

int main()
{
    string correctPassword = "Hello";
    bool loginSuccessful = false;
    string userInput;

    cout << "Please enter your password: ";

    for (int i = 1; i <= 5; i++)
    {
        cin >> userInput;
        if (userInput == correctPassword)
        {
            loginSuccessful = true;
            break;
        } else {
            cout << "wrong password\nplease try again: ";
        }

        if (i == 4) // this just a warning note before the last try
            cout << "\n\nwarning, you have one try left: ";
    }

    if (!loginSuccessful)
    {
        cout << "\n\nyou failed to log in, please leave" << endl;
        return 0;
    }

    cout << "\n\ncorrect !!     welcome to the programe :D !!";

    // the password-secured program code here

    return 0;
}