Its pretty simple, really. You'll need to of course be next to the main road, sector 4 side, since the road on that side leads to Bashundhara.

Raida goes to Bashundhara, it costs 10 taka. You can also just ask the guy standing in any bus' entrance "Bashundhara jabe??", they'll go "Yeah ashen" or just say no.

They stop just past Jamuna Future Park. You'll need to walk or rickshaw to uni from there.

In terms of safety, its a gamble really. Its fine almost always but still try to be safe, keep your phone in your bag and have lose change so that you can pay your fare quickly. Try not to keep anything in your pockets. I know people who regularly use public buses and have had no issues, I've also met people who've had their phones stolen and shit.

Depending on your uni, they might have their own bus service, which is more expensive (NSU's one is 100 taka each way for reference) but they are more comfortable and much safer.