Linear Equation in Two Variables Solver using Python
Some comments:


Rename functions to follow the PEP8 naming convention, here.
Do not use range to iterate over the a list of elements, iterate directly over it. If you need the index, as in your case, use enumerate.
No need to wrap the boolean clauses in parenthesis, moreover you can use the truth(y) values directly, see truth value testing.
Is possible add comments on what does the function does.


After a first rewrite the code of your function should look something like this:

def get_index(a, b):
    """Get the index of and element or else return 'not found' """
    status = 0
    index = 0
    for i, element in enumerate(b):
        if element == a:
            index = i
            status = 1
            break
    if status:
        return index
    else:
        return "not found"


def get_string(a, b, c):
    """Build a sub-string from c starting on a"""
    string = c[a]
    for i in range(a + 1, b, 1):
        element = c[i]
        string = string + element
    return string


def lcm(a, b):
    """Find the least common multiple"""
    if a &gt; b:
        larger = a
    else:
        larger = b
    i = larger
    while True:
        if (i % a == 0) and (i % b == 0):
            break
        else:
            i += larger
    return i


if __name__ == "__main__":
    assert get_index(1, [1, 2, 3]) == 0
    assert get_index(1, [2, 3]) == "not found"
    assert get_string(0, 3, "hello world") == "hel"
    assert lcm(2, 5) == 10


I added some (basic) test, to validate any further change you could make in the future to this functions. 

The above comments are superficial, if you want speed and reliability use the functions provided by the standard library, in the end your functions should look like something like this:

from math import gcd


def get_index(a, b):
    """Get the index of and element or else return 'not found' """
    try:
        return b.index(a)
    except ValueError:
        return "not found"


def get_string(a, b, c):
    """Build a sub-string from c starting on a"""
    return c[a:b]


def lcm(a, b):
    """Find the least common multiple"""
    return abs(a * b) // gcd(a, b)


The lcm implementation uses the gcd, see more in the wikipedia page.