Apply on the company's site
StackHike lists the role and links you to the employer. Your application goes to them. Find the role on the job board and use their apply link.
Note the day you applied
On the job page, mark the role as applied. That note is private to you. It is how you remember the date, so you do not follow up twice by accident.
Wait, then send one note
A week is a fair wait for most roles. One short message is enough: the role title, the day you applied, and a sentence on why you fit. Send it the way the posting asks, usually the address on the company's page. Another message a few days later rarely helps.
Use the wait
Read that company's interview prep, and rehearse a mock interview if you want the practice. If you have not checked whether the resume text is readable, the resume check does that in your browser before you write to anyone.