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Hello NES DEV

I have a question related to this timing diagram
http://wiki.nesdev.com/w/images/d/d1/Ntsc_timing.png

I now understand it for except a small thing , what happens when the ppu starts up ( or resets ) ? i think it starts at scanline 0 but this will make the first 2 tiles , sprites on this scanline won't go well

I understand that after the first frame, everything will go well but I am talking about the first scanline in the first frame after reseting or powering up generally.

On a real PPU, it locks itself for a frame. You can't enable rendering until it has 'warmed up', or has run for 261 scanlines worth of time.
In the mean time, it's drawing a solid screen due to rendering being disabled, usually color 00 (gray).

On a real PPU, it locks itself for a frame or two. You can't enable rendering until it has 'warmed up' over two vblanks worth of time.

what do you mean exactly by " it locks itself " and " warmed up " ?

another question , what about the emulation ? does it also the same as the real ?

I mean that the PPU will ignore any write from the CPU until 261 scanlines have passed from power on.
It's stuck in its default state (rendering disabled (forced blanking), vblank interrupts disabled, scroll set to zero, etc...)