Well…I found that some people are not familiar with grammar causative, so I think I have to make it clear for anyone for further study.
Let’s begin with Verb+たい to express that you want to do something.
ex. 話す Hanasu (talk) » 話します Hanashimasu (talk (polite))» 話したい Hanashitai
In this case you can just replace ます with たい.
ex:
先生、話したいことがありますので、少しお時間よろしいでしょうか。
Teacher, I wanna discuss something with you. Do you have time to talk?
In case you want something, you can use ほしい as for stater. (Actually there are many forms of expressing desires but I will start with simple ones)
ex. … ga hoshii
新しい靴がほしいの。
I want new shoes.
If you wanna express that you let someone do something or want people to allow you to do some actions, let’s use seru/saseru
ex. person に + object を + verb せる/させる
殺す korosu (kill) » 殺します koroshimasu (kill (polite))» 殺さない korosanai (not kill) » 殺させる (let (someone) kill)
神よ、私に敵を殺させてください。
Lord, please let me kill my enemy.
魔王よ、仲間を絶対に殺させやしない!
Overlord, I’m not going to let you kill my comrade!
(I’m just into yuusha<->maou things these days „V_V„)
寝る neru (sleep) » 寝ます nemasu » 寝ない nenai (not sleep) » 寝させる nesaseru (let (someone)sleep)
疲れた~。お袋 ちょっと寝させて。後で宿題をするから!
I’m tired. Mother, Let’s me sleep for a bit. I will do my homework later, ok?