Never build SQL by gluing user input into the string:

name = input("Name: ")
con.execute(f"SELECT * FROM users WHERE name = '{name}'")   # never do this

If someone types x' OR '1'='1, the query becomes ... WHERE name = 'x' OR '1'='1', which matches every user. Worse inputs can delete whole tables. This is SQL injection, one of the most common security holes in real software. Placeholders make it impossible, because the values are sent separately and are never treated as SQL:

import sqlite3

con = sqlite3.connect(":memory:")
con.execute("CREATE TABLE users (name TEXT, secret TEXT)")
con.executemany("INSERT INTO users VALUES (?, ?)", [("ada", "a1"), ("bo", "b2")])

evil = "x' OR '1'='1"
unsafe = con.execute(f"SELECT name FROM users WHERE name = '{evil}'").fetchall()
safe = con.execute("SELECT name FROM users WHERE name = ?", (evil,)).fetchall()
print("unsafe:", unsafe)
print("safe:", safe)